This question tests your understanding of the law of conservation of mass—the principle that mass is neither created nor destroyed in chemical reactions, only rearranged as atoms reorganize into different substances. The law of conservation of mass states that the total mass of all reactants must equal the total mass of all products because atoms are not created or destroyed in chemical reactions, merely rearranged: if you start with 50 atoms of various types (in molecules as reactants), you end with those same 50 atoms (now in molecules as products), and since mass comes from atoms, the total mass stays constant. This is why balanced equations work—they ensure atom counts match on both sides, which guarantees mass conservation. However, in OPEN systems where gases can escape or be absorbed from the air, the MEASURED mass may appear to change even though total mass is actually conserved—you just have to account for gases that left or entered the system! In this open system (moist air), the steel wool reacts with oxygen to form iron oxide, increasing the measured mass from 30 g to 38 g because 8 g of oxygen from the air was absorbed into the solid rust. Choice B correctly applies conservation of mass by recognizing that oxygen was added from the air in an open system, increasing the measured mass while total mass (including air) is conserved. For example, choice A fails because it claims new iron atoms were created, but atoms are conserved, and the increase comes from added oxygen atoms. Using conservation of mass: (1) In CLOSED systems (sealed container, nothing escapes): total mass before = total mass after, always! Add all reactant masses, add all product masses, they should match exactly. If they don't in data, measurement error occurred. (2) In OPEN systems (reaction in open air, unsealed): APPARENT mass may change because gases escape or enter. Mass INCREASE: gas from air absorbed (oxygen combining with substance during burning, rusting). Mass DECREASE: gas released to air (CO2, H2O vapor from combustion escaping). True total mass (including gases) still conserved, but you need to account for the gas! (3) To verify conservation: list ALL substances including gases. Example: burning 10g wood in open air leaves 1g ash—where did 9g go? Answer: 9g became CO2 and H2O vapor (gases escaped). Total: 10g wood + oxygen from air → 1g ash + 9g gases. Mass conserved when all counted! The "why mass appears to change" explanation: (1) Identify if system is open or closed. (2) If closed and mass changes in data, error occurred (conservation violated only by measurement mistakes). (3) If open and mass increases, look for gas absorption (combining with oxygen from air is most common). (4) If open and mass decreases, look for gas release (CO2, H2O vapor, or other gases escaping). (5) Explain: "Mass appears to decrease but is actually conserved because [specific gas] escaped; if measured in closed system, that gas would be captured and total mass would be constant." This accounting explains apparent violations while affirming conservation!

This question tests your understanding of the law of conservation of mass—the principle that mass is neither created nor destroyed in chemical reactions, only rearranged as atoms reorganize into different substances. The law of conservation of mass states that the total mass of all reactants must equal the total mass of all products because atoms are not created or destroyed in chemical reactions, merely rearranged: if you start with 50 atoms of various types (in molecules as reactants), you end with those same 50 atoms (now in molecules as products), and since mass comes from atoms, the total mass stays constant. This is why balanced equations work—they ensure atom counts match on both sides, which guarantees mass conservation. However, in OPEN systems where gases can escape or be absorbed from the air, the MEASURED mass may appear to change even though total mass is actually conserved—you just have to account for gases that left or entered the system! In this sealed jar (closed system), the total reactant mass is $40 , \mathrm{g} , \mathrm{AgNO_3} , \text{solution} + 40 , \mathrm{g} , \mathrm{NaCl} , \text{solution} = 80 , \mathrm{g}$, and after the precipitate forms, the total product mass (AgCl solid + NaNO3 solution) should remain 80 g since nothing escapes. Choice A correctly applies conservation of mass by recognizing that in a closed system, total mass is conserved at 80 g. For example, choice D fails because it suggests mass increases when a new compound forms, but conservation means mass stays the same regardless of new compounds. Using conservation of mass: (1) In CLOSED systems (sealed container, nothing escapes): total mass before = total mass after, always! Add all reactant masses, add all product masses, they should match exactly. If they don't in data, measurement error occurred. (2) In OPEN systems (reaction in open air, unsealed): APPARENT mass may change because gases escape or enter. Mass INCREASE: gas from air absorbed (oxygen combining with substance during burning, rusting). Mass DECREASE: gas released to air (CO2, H2O vapor from combustion escaping). True total mass (including gases) still conserved, but you need to account for the gas! (3) To verify conservation: list ALL substances including gases. Example: burning 10g wood in open air leaves 1g ash—where did 9g go? Answer: 9g became CO2 and H2O vapor (gases escaped). Total: 10g wood + oxygen from air → 1g ash + 9g gases. Mass conserved when all counted! The "why mass appears to change" explanation: (1) Identify if system is open or closed. (2) If closed and mass changes in data, error occurred (conservation violated only by measurement mistakes). (3) If open and mass increases, look for gas absorption (combining with oxygen from air is most common). (4) If open and mass decreases, look for gas release (CO2, H2O vapor, or other gases escaping). (5) Explain: "Mass appears to decrease but is actually conserved because [specific gas] escaped; if measured in closed system, that gas would be captured and total mass would be constant." This accounting explains apparent violations while affirming conservation!

This question tests your understanding of the law of conservation of mass—the principle that mass is neither created nor destroyed in chemical reactions, only rearranged as atoms reorganize into different substances. The law of conservation of mass states that the total mass of all reactants must equal the total mass of all products because atoms are not created or destroyed in chemical reactions, merely rearranged: if you start with 50 atoms of various types (in molecules as reactants), you end with those same 50 atoms (now in molecules as products), and since mass comes from atoms, the total mass stays constant. This is why balanced equations work—they ensure atom counts match on both sides, which guarantees mass conservation. However, in OPEN systems where gases can escape or be absorbed from the air, the MEASURED mass may appear to change even though total mass is actually conserved—you just have to account for gases that left or entered the system! In Trial 1 (open), CO2 gas escapes, causing a 4 g decrease from 150 g to 146 g, while in Trial 2 (sealed), the gas is trapped, keeping the mass at 150 g; total mass is conserved in both, but the open system shows apparent loss. Choice B correctly applies conservation of mass by recognizing the role of the open vs. closed system in whether gas escape affects measured mass. Choice A fails because it suggests atoms were destroyed in Trial 1, violating conservation—in reality, atoms are conserved, but the gas left the measured system in the open trial. Using conservation of mass: (1) In CLOSED systems (sealed container, nothing escapes): total mass before = total mass after, always! Add all reactant masses, add all product masses, they should match exactly. If they don't in data, measurement error occurred. (2) In OPEN systems (reaction in open air, unsealed): APPARENT mass may change because gases escape or enter. Mass INCREASE: gas from air absorbed (oxygen combining with substance during burning, rusting). Mass DECREASE: gas released to air (CO2, H2O vapor from combustion escaping). True total mass (including gases) still conserved, but you need to account for the gas! (3) To verify conservation: list ALL substances including gases. Example: burning 10g wood in open air leaves 1g ash—where did 9g go? Answer: 9g became CO2 and H2O vapor (gases escaped). Total: 10g wood + oxygen from air → 1g ash + 9g gases. Mass conserved when all counted! The "why mass appears to change" explanation: (1) Identify if system is open or closed. (2) If closed and mass changes in data, error occurred (conservation violated only by measurement mistakes). (3) If open and mass increases, look for gas absorption (combining with oxygen from air is most common). (4) If open and mass decreases, look for gas release (CO2, H2O vapor, or other gases escaping). (5) Explain: "Mass appears to decrease but is actually conserved because [specific gas] escaped; if measured in closed system, that gas would be captured and total mass would be constant." This accounting explains apparent violations while affirming conservation! Terrific comparison of trials—you've got this!

This question tests your understanding of the law of conservation of mass—the principle that mass is neither created nor destroyed in chemical reactions, only rearranged as atoms reorganize into different substances. The law of conservation of mass states that the total mass of all reactants must equal the total mass of all products because atoms are not created or destroyed in chemical reactions, merely rearranged: if you start with 50 atoms of various types (in molecules as reactants), you end with those same 50 atoms (now in molecules as products), and since mass comes from atoms, the total mass stays constant. This is why balanced equations work—they ensure atom counts match on both sides, which guarantees mass conservation. However, in OPEN systems where gases can escape or be absorbed from the air, the MEASURED mass may appear to change even though total mass is actually conserved—you just have to account for gases that left or entered the system! In this sealed container, the reaction changes 3 gas molecules (2H2 + O2) into 2 liquid molecules, but the total mass remains 80 g because the same atoms (4 H and 2 O) are present before and after, just rearranged. Choice B correctly applies conservation of mass by recognizing that mass depends on atoms, not the number of molecules, so it stays constant despite the molecule count change. Choice A fails because it supports the student's incorrect claim that fewer molecules mean less mass, but conservation is about atoms, and the sealed system shows no mass change. Using conservation of mass: (1) In CLOSED systems (sealed container, nothing escapes): total mass before = total mass after, always! Add all reactant masses, add all product masses, they should match exactly. If they don't in data, measurement error occurred. (2) In OPEN systems (reaction in open air, unsealed): APPARENT mass may change because gases escape or enter. Mass INCREASE: gas from air absorbed (oxygen combining with substance during burning, rusting). Mass DECREASE: gas released to air (CO2, H2O vapor from combustion escaping). True total mass (including gases) still conserved, but you need to account for the gas! (3) To verify conservation: list ALL substances including gases. Example: burning 10g wood in open air leaves 1g ash—where did 9g go? Answer: 9g became CO2 and H2O vapor (gases escaped). Total: 10g wood + oxygen from air → 1g ash + 9g gases. Mass conserved when all counted! The "why mass appears to change" explanation: (1) Identify if system is open or closed. (2) If closed and mass changes in data, error occurred (conservation violated only by measurement mistakes). (3) If open and mass increases, look for gas absorption (combining with oxygen from air is most common). (4) If open and mass decreases, look for gas release (CO2, H2O vapor, or other gases escaping). (5) Explain: "Mass appears to decrease but is actually conserved because [specific gas] escaped; if measured in closed system, that gas would be captured and total mass would be constant." This accounting explains apparent violations while affirming conservation! Wonderful insight on atoms vs. molecules—keep thinking at that level!

This question tests your understanding of the law of conservation of mass—the principle that mass is neither created nor destroyed in chemical reactions, only rearranged as atoms reorganize into different substances. The law of conservation of mass states that the total mass of all reactants must equal the total mass of all products because atoms are not created or destroyed in chemical reactions, merely rearranged: if you start with 50 atoms of various types (in molecules as reactants), you end with those same 50 atoms (now in molecules as products), and since mass comes from atoms, the total mass stays constant. This is why balanced equations work—they ensure atom counts match on both sides, which guarantees mass conservation. However, in OPEN systems where gases can escape or be absorbed from the air, the MEASURED mass may appear to change even though total mass is actually conserved—you just have to account for gases that left or entered the system! In this open grill, the 25 g charcoal reacts with oxygen from air to form mostly CO2 gas (escaping) and 2 g ash, so the 23 g difference is in the escaped gases, but total mass including them and the oxygen input conserves the overall mass. Choice B correctly applies conservation of mass by recognizing that in open systems, apparent decreases occur when gaseous products like CO2 escape and are not measured. Choice A fails by claiming atoms are destroyed, which violates the law since carbon atoms rearrange into CO2; choices C and D incorrectly attribute the change to heat or volume, but heat lacks mass, and volume doesn't affect mass conservation. Using conservation of mass: (1) In CLOSED systems (sealed container, nothing escapes): total mass before = total mass after, always! Add all reactant masses, add all product masses, they should match exactly. If they don't in data, measurement error occurred. (2) In OPEN systems (reaction in open air, unsealed): APPARENT mass may change because gases escape or enter. Mass INCREASE: gas from air absorbed (oxygen combining with substance during burning, rusting). Mass DECREASE: gas released to air (CO2, H2O vapor from combustion escaping). True total mass (including gases) still conserved, but you need to account for the gas! (3) To verify conservation: list ALL substances including gases. Example: burning 10g wood in open air leaves 1g ash—where did 9g go? Answer: 9g became CO2 and H2O vapor (gases escaped). Total: 10g wood + oxygen from air → 1g ash + 9g gases. Mass conserved when all counted! The "why mass appears to change" explanation: (1) Identify if system is open or closed. (2) If closed and mass changes in data, error occurred (conservation violated only by measurement mistakes). (3) If open and mass increases, look for gas absorption (combining with oxygen from air is most common). (4) If open and mass decreases, look for gas release (CO2, H2O vapor, or other gases escaping). (5) Explain: "Mass appears to decrease but is actually conserved because [specific gas] escaped; if measured in closed system, that gas would be captured and total mass would be constant." This accounting explains apparent violations while affirming conservation!

This question tests your understanding of the law of conservation of mass—the principle that mass is neither created nor destroyed in chemical reactions, only rearranged as atoms reorganize into different substances. The law of conservation of mass states that the total mass of all reactants must equal the total mass of all products because atoms are not created or destroyed in chemical reactions, merely rearranged: if you start with 50 atoms of various types (in molecules as reactants), you end with those same 50 atoms (now in molecules as products), and since mass comes from atoms, the total mass stays constant. This is why balanced equations work—they ensure atom counts match on both sides, which guarantees mass conservation. However, in OPEN systems where gases can escape or be absorbed from the air, the MEASURED mass may appear to change even though total mass is actually conserved—you just have to account for gases that left or entered the system! In this open container, the mass drops from 20 g to 17 g likely because about 3 g of gaseous product escaped, but if included, total mass would conserve at 20 g. Choice C correctly applies conservation of mass by recognizing that in open systems, apparent missing mass is often due to escaped gases not measured, but the law holds when accounting for them. Choice B fails by claiming atoms disappeared, which violates atom conservation; choice A suggests mass destruction due to stability, but mass is independent of stability, and choice D incorrectly states mass always appears constant even in open systems, ignoring gas effects. Using conservation of mass: (1) In CLOSED systems (sealed container, nothing escapes): total mass before = total mass after, always! Add all reactant masses, add all product masses, they should match exactly. If they don't in data, measurement error occurred. (2) In OPEN systems (reaction in open air, unsealed): APPARENT mass may change because gases escape or enter. Mass INCREASE: gas from air absorbed (oxygen combining with substance during burning, rusting). Mass DECREASE: gas released to air (CO2, H2O vapor from combustion escaping). True total mass (including gases) still conserved, but you need to account for the gas! (3) To verify conservation: list ALL substances including gases. Example: burning 10g wood in open air leaves 1g ash—where did 9g go? Answer: 9g became CO2 and H2O vapor (gases escaped). Total: 10g wood + oxygen from air → 1g ash + 9g gases. Mass conserved when all counted! The "why mass appears to change" explanation: (1) Identify if system is open or closed. (2) If closed and mass changes in data, error occurred (conservation violated only by measurement mistakes). (3) If open and mass increases, look for gas absorption (combining with oxygen from air is most common). (4) If open and mass decreases, look for gas release (CO2, H2O vapor, or other gases escaping). (5) Explain: "Mass appears to decrease but is actually conserved because [specific gas] escaped; if measured in closed system, that gas would be captured and total mass would be constant." This accounting explains apparent violations while affirming conservation!

This question tests your understanding of the law of conservation of mass—the principle that mass is neither created nor destroyed in chemical reactions, only rearranged as atoms reorganize into different substances. The law of conservation of mass states that the total mass of all reactants must equal the total mass of all products because atoms are not created or destroyed in chemical reactions, merely rearranged: if you start with 50 atoms of various types (in molecules as reactants), you end with those same 50 atoms (now in molecules as products), and since mass comes from atoms, the total mass stays constant. This is why balanced equations work—they ensure atom counts match on both sides, which guarantees mass conservation. However, in OPEN systems where gases can escape or be absorbed from the air, the MEASURED mass may appear to change even though total mass is actually conserved—you just have to account for gases that left or entered the system! In this sealed bag (a closed system), the total mass before mixing is 85 g (10 g CaCl2 + 20 g Na2CO3 solution + bag mass implied in total), and since nothing can escape or enter, the total mass after the reaction, including the solid CaCO3 and NaCl solution, should still be 85 g. Choice B correctly applies conservation of mass by recognizing that in a closed system, total mass is conserved at 85 g. For example, choice C fails because it suggests new matter was created, violating conservation, but mass cannot be created in chemical reactions. Using conservation of mass: (1) In CLOSED systems (sealed container, nothing escapes): total mass before = total mass after, always! Add all reactant masses, add all product masses, they should match exactly. If they don't in data, measurement error occurred. (2) In OPEN systems (reaction in open air, unsealed): APPARENT mass may change because gases escape or enter. Mass INCREASE: gas from air absorbed (oxygen combining with substance during burning, rusting). Mass DECREASE: gas released to air (CO2, H2O vapor from combustion escaping). True total mass (including gases) still conserved, but you need to account for the gas! (3) To verify conservation: list ALL substances including gases. Example: burning 10g wood in open air leaves 1g ash—where did 9g go? Answer: 9g became CO2 and H2O vapor (gases escaped). Total: 10g wood + oxygen from air → 1g ash + 9g gases. Mass conserved when all counted! The "why mass appears to change" explanation: (1) Identify if system is open or closed. (2) If closed and mass changes in data, error occurred (conservation violated only by measurement mistakes). (3) If open and mass increases, look for gas absorption (combining with oxygen from air is most common). (4) If open and mass decreases, look for gas release (CO2, H2O vapor, or other gases escaping). (5) Explain: "Mass appears to decrease but is actually conserved because [specific gas] escaped; if measured in closed system, that gas would be captured and total mass would be constant." This accounting explains apparent violations while affirming conservation!

This question tests your understanding of the law of conservation of mass—the principle that mass is neither created nor destroyed in chemical reactions, only rearranged as atoms reorganize into different substances. The law of conservation of mass states that the total mass of all reactants must equal the total mass of all products because atoms are not created or destroyed in chemical reactions, merely rearranged: if you start with 50 atoms of various types (in molecules as reactants), you end with those same 50 atoms (now in molecules as products), and since mass comes from atoms, the total mass stays constant. This is why balanced equations work—they ensure atom counts match on both sides, which guarantees mass conservation. However, in OPEN systems where gases can escape or be absorbed from the air, the MEASURED mass may appear to change even though total mass is actually conserved—you just have to account for gases that left or entered the system! In this sealed container (closed system), 15 g M + 10 g Cl2 = 25 g total reactants, and since all react to form solid MCl2 with no gas left, the product mass should be 25 g. Choice C correctly applies conservation of mass by recognizing that in a closed system, the product mass equals the sum of reactant masses at 25 g. For example, choice A fails because it suggests the gas disappears without mass, but gases have mass, and here it's incorporated into the solid, conserving total mass. Using conservation of mass: (1) In CLOSED systems (sealed container, nothing escapes): total mass before = total mass after, always! Add all reactant masses, add all product masses, they should match exactly. If they don't in data, measurement error occurred. (2) In OPEN systems (reaction in open air, unsealed): APPARENT mass may change because gases escape or enter. Mass INCREASE: gas from air absorbed (oxygen combining with substance during burning, rusting). Mass DECREASE: gas released to air (CO2, H2O vapor from combustion escaping). True total mass (including gases) still conserved, but you need to account for the gas! (3) To verify conservation: list ALL substances including gases. Example: burning 10g wood in open air leaves 1g ash—where did 9g go? Answer: 9g became CO2 and H2O vapor (gases escaped). Total: 10g wood + oxygen from air → 1g ash + 9g gases. Mass conserved when all counted! The "why mass appears to change" explanation: (1) Identify if system is open or closed. (2) If closed and mass changes in data, error occurred (conservation violated only by measurement mistakes). (3) If open and mass increases, look for gas absorption (combining with oxygen from air is most common). (4) If open and mass decreases, look for gas release (CO2, H2O vapor, or other gases escaping). (5) Explain: "Mass appears to decrease but is actually conserved because [specific gas] escaped; if measured in closed system, that gas would be captured and total mass would be constant." This accounting explains apparent violations while affirming conservation!

This question tests your understanding of the law of conservation of mass—the principle that mass is neither created nor destroyed in chemical reactions, only rearranged as atoms reorganize into different substances. The law of conservation of mass states that the total mass of all reactants must equal the total mass of all products because atoms are not created or destroyed in chemical reactions, merely rearranged: if you start with 50 atoms of various types (in molecules as reactants), you end with those same 50 atoms (now in molecules as products), and since mass comes from atoms, the total mass stays constant. This is why balanced equations work—they ensure atom counts match on both sides, which guarantees mass conservation. However, in OPEN systems where gases can escape or be absorbed from the air, the MEASURED mass may appear to change even though total mass is actually conserved—you just have to account for gases that left or entered the system! Heating 15 g of CaCO3 in an open flask produces 9 g of CaO and 6 g of CO2 gas that escapes, so the measured mass in the flask decreases, but total mass including the escaped gas would still be 15 g. Choice A correctly applies conservation of mass by recognizing that the missing mass is the escaped CO2, and in a closed system, total mass would be conserved. Choice B fails because it suggests mass was destroyed in decomposition, but conservation holds—atoms are rearranged, and the gas simply left the system without being measured. Using conservation of mass: (1) In CLOSED systems (sealed container, nothing escapes): total mass before = total mass after, always! Add all reactant masses, add all product masses, they should match exactly. If they don't in data, measurement error occurred. (2) In OPEN systems (reaction in open air, unsealed): APPARENT mass may change because gases escape or enter. Mass INCREASE: gas from air absorbed (oxygen combining with substance during burning, rusting). Mass DECREASE: gas released to air (CO2, H2O vapor from combustion escaping). True total mass (including gases) still conserved, but you need to account for the gas! (3) To verify conservation: list ALL substances including gases. Example: burning 10g wood in open air leaves 1g ash—where did 9g go? Answer: 9g became CO2 and H2O vapor (gases escaped). Total: 10g wood + oxygen from air → 1g ash + 9g gases. Mass conserved when all counted! The "why mass appears to change" explanation: (1) Identify if system is open or closed. (2) If closed and mass changes in data, error occurred (conservation violated only by measurement mistakes). (3) If open and mass increases, look for gas absorption (combining with oxygen from air is most common). (4) If open and mass decreases, look for gas release (CO2, H2O vapor, or other gases escaping). (5) Explain: "Mass appears to decrease but is actually conserved because [specific gas] escaped; if measured in closed system, that gas would be captured and total mass would be constant." This accounting explains apparent violations while affirming conservation! Fantastic— you're nailing these decomposition examples!

This question tests your understanding of the law of conservation of mass—the principle that mass is neither created nor destroyed in chemical reactions, only rearranged as atoms reorganize into different substances. The law of conservation of mass states that the total mass of all reactants must equal the total mass of all products because atoms are not created or destroyed in chemical reactions, merely rearranged: if you start with 50 atoms of various types (in molecules as reactants), you end with those same 50 atoms (now in molecules as products), and since mass comes from atoms, the total mass stays constant. This is why balanced equations work—they ensure atom counts match on both sides, which guarantees mass conservation. However, in OPEN systems where gases can escape or be absorbed from the air, the MEASURED mass may appear to change even though total mass is actually conserved—you just have to account for gases that left or entered the system! In this open beaker setup, the initial mass is 120 g, and after the reaction, it's 116 g, but the 4 g difference is due to CO2 gas escaping into the air, so the total mass including the escaped gas would still equal 120 g if captured. Choice B correctly applies conservation of mass by recognizing that in open systems, apparent mass decreases occur when gases like CO2 escape, but true mass is conserved when accounting for them. Choice A fails by incorrectly claiming matter is destroyed, which violates the law since atoms are only rearranged, not eliminated; similarly, choices C and D overlook the role of gases and misattribute the change to liquids or volume, but mass conservation holds independently of state or volume changes. Using conservation of mass: (1) In CLOSED systems (sealed container, nothing escapes): total mass before = total mass after, always! Add all reactant masses, add all product masses, they should match exactly. If they don't in data, measurement error occurred. (2) In OPEN systems (reaction in open air, unsealed): APPARENT mass may change because gases escape or enter. Mass INCREASE: gas from air absorbed (oxygen combining with substance during burning, rusting). Mass DECREASE: gas released to air (CO2, H2O vapor from combustion escaping). True total mass (including gases) still conserved, but you need to account for the gas! (3) To verify conservation: list ALL substances including gases. Example: burning 10g wood in open air leaves 1g ash—where did 9g go? Answer: 9g became CO2 and H2O vapor (gases escaped). Total: 10g wood + oxygen from air → 1g ash + 9g gases. Mass conserved when all counted! The "why mass appears to change" explanation: (1) Identify if system is open or closed. (2) If closed and mass changes in data, error occurred (conservation violated only by measurement mistakes). (3) If open and mass increases, look for gas absorption (combining with oxygen from air is most common). (4) If open and mass decreases, look for gas release (CO2, H2O vapor, or other gases escaping). (5) Explain: "Mass appears to decrease but is actually conserved because [specific gas] escaped; if measured in closed system, that gas would be captured and total mass would be constant." This accounting explains apparent violations while affirming conservation!