During digestion, the energy in food is converted to energy the body can use. Scientists use calorimetry experiments to measure the calories, or energy, provided by food when it is digested or burned.

The relationship used to find the heat transferred energy is given by , where is the mass of the material, is the given specific heat capacity, and is the change in temperature of the material.

In this experiment, food was burned over a Bunsen burner under a can of 200 ml of water. The temperature change of the water and mass change of the food can be used to determine the calories in four different food items.

Table 1 shows the values of the change of mass of the food items, the change in temperature of the water and the energy. Table 2 shows the energy to mass ratio of three of those food items.

Table 1

Roasted Peanut Peanut Cracker Cheese Puff

Water Temp. Initial 23.9 °C 33.2 °C 40.3 °C 53.9 °C

Water Temp. Final 30.0 °C 40.9 °C 55.9 °C 62.8 °C

Food Mass Initial 0.69 g 0.61 g 3.21 g 1.22 g

Food Mass Final 0.38 g 0.21 g 0.91 g 0.48 g

Energy 1.22 Cal 1.54 Cal 3.12 Cal 1.78 Cal

Table 2

Sample Energy to Mass Ratio (Cal/g)

1 1.36

2 3.93

3 2.40

Based on the results shown in Table 1 from the experiment, what is the relationship between the mass change of the food sample and the calories in the food?

When describing their behavior, gases are typically treated as "ideal gases" in what is known as the ideal gas law. Two science students describe the ideal gas law in their own terms:

Student 1: The ideal gas law is based on the assumptions that a gas consists of a large number of molecules and that gas molecules take up negligible space in a gas due to their minuscule size in comparison to the space between each gas molecule. Also important is the assumption that all of the forces acting on gas molecules are from collisions with other gas molecules or a container and not from anything else. According to the ideal gas law, all gases behave the same so long as those assumptions hold true. Therefore, if you measure the volume of helium gas at a certain temperature and pressure, an equivalent amount of radon gas (a much heavier gas) at the same conditions will have the same volume.

Student 2: The ideal gas law's primary assumption is that a gas consists of a very large number of particles. For example, even within a single bacteria there can be billions of gas molecules despite the bacteria's very small size. Therefore, in a room full of gas, there are so many particles that their random behavior is, on average, uniform. There are exceptions to the ideal gas law and those are gases with very high inter-molecular forces of attraction (IMFAs). A gas with high IMFA will behave very differently than a gas with a low IMFA. As one could imagine, because a gas with a high IMFA will have molecules that tend to attract each other, that gas will display a lower volume than that which would be predicted by the ideal gas law.

Assuming that both students' statements are correct in describing the ideal gas law, how would we then describe the effects of molecule size and IMFAs on a gas's volume?

Two students are studying hydrocarbon combustion, or the burning of compounds containing carbon and hydrogen in the presence of oxygen gas. Both students express their views on this phenomenon.

Student 1: Hydrocarbons are high in energy and therefore naturally burn in order to release that energy. That energy is released in the form of light and heat. If water is thrown onto a fire, it will extinguish it because it cuts the combustion from the oxygen gas required for it to burn.

Student 2: Hydrocarbons are compounds at a greater energy state than the compounds produced when they burn. This excess energy changes to heat when hydrocarbons burn. Lastly, hydrocarbons require a spark to initiate the combustion.

Which of the following statements would both students be most likely to agree?

In studying the effects of adding heat to different substances on each substance's temperature, a researcher conducted the following experiment. The researcher added 1,000 Joules of energy by a controlled heat lamp to four different substances. The temperature change in each substance that was caused by the heat was then measured and recorded. The results of this experiment are shown below.

The researcher is aware of a concept called specific heat and knows that lead has a lower specific heat than wood, which has a lower specific heat than cardboard, which has a lower specific heat than styrofoam. Therefore, the researcher has ordered the objects in the table from lowest specific heat (lead) to highest (styrofoam).

According to the data in the table, what is the apparent relationship between specific heat and the amount that an object's temperature changes when a given amount of heat is added?

There are two types of forces that occur with all substances on Earth. Intramolecular forces occur between atoms in a molecule, while intermolecular forces occur between neighboring molecules. Intermolecular forces can be dipole-dipole forces, hydrogen bonding, or London dispersion forces.

Professor 1:

Water molecules represent an example of hydrogen bonding due to the attraction between the hydrogen atoms and the oxygen atoms in the molecule. This strong dipole-dipole occurs due to lone pairs present on such atoms as Fluorine, Nitrogen, and Oxygen, which are able to pair more closely to the hydrogen atom in another nearby molecule. Water can be present in a solid, liquid, or gaseous state on Earth depending on the competition between the strength of intermolecular bonds and the thermal energy of the system. In 1873, a Dutch scientist, Van der Waals derived an equation that included both the force of attraction between the particles of a gas and the volume of the particles at high pressures. This equation led to a better fit for experimental data than the Ideal Gas Law.

Professor 2:

Water is the only substance on Earth that we routinely encounter as a solid, liquid, and gas. At low temperatures, the water molecules lock into a rigid structure, but as the temperature increases, the average kinetic energy of the water molecules increases and the molecules are able to move more creating its other natural states of matter. The higher the temperature, the more likely water is to be a gas. Water is proof of the kinetic theory, which assumes that there is no force of attraction between the particles of the gas state. The best fit for experimental data involving water in a gaseous form is found by using the Ideal Gas Law, since there is no interaction between the gaseous molecules. This law accounts for all of the forces that occur with gases on Earth.

A 3rd professor mentions that he has he has seen Hydrogen Bonding have an effect on his experimental results. What would each professor say about his statement?

In its refined form, iron is a shiny, silver-gray metal; however, when refined iron is exposed to atmospheric conditions for an extended period of time, its surface becomes flaky, pitted, and red- or orange-colored. This process is known as "rusting," and the new flaky, orange or red substance is called "rust."

Below, two scientists discuss how rust forms and the composition of rust.

Scientist 1:

Both water and oxygen are needed for rust to form. Water is an electrolyte_,_ meaning that it allows ions to move within it. When iron comes into contact with water, some iron naturally dissociates into iron ions (Fe2+) and free electrons. Additionally, when atmospheric oxygen (O2) dissolves in water, some oxygen reacts with water to form hydroxide ions (OH-). Because water allows ions to move freely, iron ions and hydroxide ions combine to form a new compound: iron hydroxide. However, iron hydroxide is not a stable compound. Over time, as water evaporates, it changes into a hydrated form of iron oxide. This is rust.

Salts can act as catalysts for rust formation, meaning that they speed up the rate at which rust forms. However, rust can form in pure water, in the absence of added salts.

Increasing the ambient temperature increases the rate of rust formation. Additionally, increasing the amount of iron's surface area that is exposed to water also increases the rate at which rust forms. However, because a layer of rust is porous to water and oxygen, water and oxygen will continue to cause the interior of a piece of iron to rust even after the iron's surface has been rusted.

Scientist 2:

Attack by acids causes rust to form. In water, acids ionize to create positively-charged hydronium (H+) ions and negatively-charged anions. Hydronium ions are electron-deficient; because of this, they attract electrons from iron. This creates iron ions (Fe2+), which are soluble in water. Once dissolved in water, iron ions react with dissolved atmospheric oxygen (O2) to create iron oxide, or rust.

Acids can come from a variety of sources. For example, when carbon dioxide in the atmosphere dissolves in water, carbonic acid (H2CO3) is created. Carbonic acid is the most common cause of rusting. However, other environmental sources of acids exist. Rainwater is normally slightly acidic because it has come into contact with molecules in the atmosphere, like sulfur dioxide and nitrogen oxides. These molecules also dissolve in water to form acids. Additionally, iron itself may contain impurities such as phosphorous and sulfur, which react with water to produce acids. Both acidic environments and impurities within iron itself create the conditions under which iron rusts.

Rusting can be prevented by painting the surface of iron, thus preventing it from coming into contact with water, oxygen, and acids. Iron can also be protected in a process called "galvanizing," which involves coating iron in a thin layer of zinc. Because zinc is more reactive than iron, it is corroded while the iron is protected.

An iron nail is placed in a test tube filled with water. Then, a layer of oil is poured over the water. After an extended period of time, no rust is observed to have formed on the iron nail. Scientist 1 would most likely explain this result by saying that:

Acids and bases are chemical substances that react with each other and certain other elements to produce compounds like salts. Chemists have discussed the unique reaction between acids and bases significantly, here are three major theories that attempt to explain how acids and bases react.

Theory 1: The Arrhenius acid/base theory focuses on hydrogen, and how acids and bases neutralize each other to form salt and water. Acids dissociate in a solution into hydrogen ions , while bases dissociate in a solution into hydroxide ions . An acid, when introduced to water, will increase the amount of hydrogen ions present (which can be observed as hydronium ions), or decrease the amount of hydroxide ions present. Conversely, a base will either increase the amount of hydroxide ions or decrease the amount of hydronium ions when introduced to water. This is the only way to determine if a substance is an acid or base. When an acid is introduced to a base, a neutralization reaction occurs when the protons of the acid combine with the hydroxide ions of the base to form water and a salt byproduct.

Theory 2: The Bronsted-Lowry theory concerns the donation of hydrogen ions from acids to bases and the formation of conjugate pairs. This theory defines acids as the substance that donates a proton, and bases as the substance that accepts the proton. Because reactions can be reversible, acids that have their hydrogen ion removed become that acid’s conjugate base, while bases that receive that hydrogen ion become the original base’s conjugate acid. This is true because if the reaction is reversed, the former-acid with its missing proton will be receiving the hydrogen ion (making it the base) and the former-base with the additional proton will be donating it (making it the acid). Reactions then produce new bases and acids, and do not neutralize to produce salts and water. This acid-base theory does not require a solvent.

Theory 3: The Lewis theory discards the concern with hydrogen ions and focuses on electron-pair donation. According to this theory, acids are substances that can receive an electron pair whereas bases are substances that can donate an electron pair. This broadens the consideration of what is a base or an acid even further, eliminating the need to define substances based on their use of a hydrogen ion. Compounds that have vacancies in their electron octets can be considered Lewis acids, and compounds with extra electrons in their octets can be considered Lewis bases.

Which theory would consider boron trifluoride an acid?

In its refined form, iron is a shiny, silver-gray metal; however, when refined iron is exposed to atmospheric conditions for an extended period of time, its surface becomes flaky, pitted, and red- or orange-colored. This process is known as "rusting," and the new flaky, orange or red substance is called "rust."

Below, two scientists discuss how rust forms and the composition of rust.

Scientist 1:

Both water and oxygen are needed for rust to form. Water is an electrolyte_,_ meaning that it allows ions to move within it. When iron comes into contact with water, some iron naturally dissociates into iron ions (Fe2+) and free electrons. Additionally, when atmospheric oxygen (O2) dissolves in water, some oxygen reacts with water to form hydroxide ions (OH-). Because water allows ions to move freely, iron ions and hydroxide ions combine to form a new compound: iron hydroxide. However, iron hydroxide is not a stable compound. Over time, as water evaporates, it changes into a hydrated form of iron oxide. This is rust.

Salts can act as catalysts for rust formation, meaning that they speed up the rate at which rust forms. However, rust can form in pure water, in the absence of added salts.

Increasing the ambient temperature increases the rate of rust formation. Additionally, increasing the amount of iron's surface area that is exposed to water also increases the rate at which rust forms. However, because a layer of rust is porous to water and oxygen, water and oxygen will continue to cause the interior of a piece of iron to rust even after the iron's surface has been rusted.

Scientist 2:

Attack by acids causes rust to form. In water, acids ionize to create positively-charged hydronium (H+) ions and negatively-charged anions. Hydronium ions are electron-deficient; because of this, they attract electrons from iron. This creates iron ions (Fe2+), which are soluble in water. Once dissolved in water, iron ions react with dissolved atmospheric oxygen (O2) to create iron oxide, or rust.

Acids can come from a variety of sources. For example, when carbon dioxide in the atmosphere dissolves in water, carbonic acid (H2CO3) is created. Carbonic acid is the most common cause of rusting. However, other environmental sources of acids exist. Rainwater is normally slightly acidic because it has come into contact with molecules in the atmosphere, like sulfur dioxide and nitrogen oxides. These molecules also dissolve in water to form acids. Additionally, iron itself may contain impurities such as phosphorous and sulfur, which react with water to produce acids. Both acidic environments and impurities within iron itself create the conditions under which iron rusts.

Rusting can be prevented by painting the surface of iron, thus preventing it from coming into contact with water, oxygen, and acids. Iron can also be protected in a process called "galvanizing," which involves coating iron in a thin layer of zinc. Because zinc is more reactive than iron, it is corroded while the iron is protected.

Given that the explanation of Scientist 2 is correct, which of the following conditions, if any, will result in the formation of rust?

Acids and bases are chemical substances that react with each other and certain other elements to produce compounds like salts. Chemists have discussed the unique reaction between acids and bases significantly, here are three major theories that attempt to explain how acids and bases react.

Theory 1: The Arrhenius acid/base theory focuses on hydrogen, and how acids and bases neutralize each other to form salt and water. Acids dissociate in a solution into hydrogen ions , while bases dissociate in a solution into hydroxide ions . An acid, when introduced to water, will increase the amount of hydrogen ions present (which can be observed as hydronium ions), or decrease the amount of hydroxide ions present. Conversely, a base will either increase the amount of hydroxide ions or decrease the amount of hydronium ions when introduced to water. This is the only way to determine if a substance is an acid or base. When an acid is introduced to a base, a neutralization reaction occurs when the protons of the acid combine with the hydroxide ions of the base to form water and a salt byproduct.

Theory 2: The Bronsted-Lowry theory concerns the donation of hydrogen ions from acids to bases and the formation of conjugate pairs. This theory defines acids as the substance that donates a proton, and bases as the substance that accepts the proton. Because reactions can be reversible, acids that have their hydrogen ion removed become that acid’s conjugate base, while bases that receive that hydrogen ion become the original base’s conjugate acid. This is true because if the reaction is reversed, the former-acid with its missing proton will be receiving the hydrogen ion (making it the base) and the former-base with the additional proton will be donating it (making it the acid). Reactions then produce new bases and acids, and do not neutralize to produce salts and water. This acid-base theory does not require a solvent.

Theory 3: The Lewis theory discards the concern with hydrogen ions and focuses on electron-pair donation. According to this theory, acids are substances that can receive an electron pair whereas bases are substances that can donate an electron pair. This broadens the consideration of what is a base or an acid even further, eliminating the need to define substances based on their use of a hydrogen ion. Compounds that have vacancies in their electron octets can be considered Lewis acids, and compounds with extra electrons in their octets can be considered Lewis bases.

Which theory would most likely consider the greatest number of substances as acids or bases?

When describing their behavior, gases are typically treated as "ideal gases" in what is known as the ideal gas law. Two science students describe the ideal gas law in their own terms:

Student 1: The ideal gas law is based on the assumptions that a gas consists of a large number of molecules and that gas molecules take up negligible space in a gas due to their minuscule size in comparison to the space between each gas molecule. Also important is the assumption that all of the forces acting on gas molecules are from collisions with other gas molecules or a container and not from anything else. According to the ideal gas law, all gases behave the same so long as those assumptions hold true. Therefore, if you measure the volume of helium gas at a certain temperature and pressure, an equivalent amount of radon gas (a much heavier gas) at the same conditions will have the same volume.

Student 2: The ideal gas law's primary assumption is that a gas consists of a very large number of particles. For example, even within a single bacteria there can be billions of gas molecules despite the bacteria's very small size. Therefore, in a room full of gas, there are so many particles that their random behavior is, on average, uniform. There are exceptions to the ideal gas law and those are gases with very high inter-molecular forces of attraction (IMFAs). A gas with high IMFA will behave very differently than a gas with a low IMFA. As one could imagine, because a gas with a high IMFA will have molecules that tend to attract each other, that gas will display a lower volume than that which would be predicted by the ideal gas law.

An experiment was carried out that measured the volumes of two very small quantities of gases, hydrogen and tetrachloromethane. Both gases have a dipole moment of zero, meaning they do not exhibit intermolecular forces of attraction. Hydrogen is the lightest known gas, while tetrachloromethane is much heavier and therefore has much larger molecules.

The experiment yielded the following result: the same number of hydrogen molecules occupied a slightly different volume than an equivalent quantity of tetrachloromethane. This remained true only for small quantities of both gases.

What does this experimental data mean with regard to the opinions of the two students above?