Determine whether a chemical reaction has occurred

Example Question #1 : Determine Whether A Chemical Reaction Has Occurred

Heating Zinc Chloride to its melting point of 290 °C and watching it turn to a liquid is an example of:

Possible Answers:

neither a physical nor a chemical change

both a physical and chemical change

a physical change

a chemical change

Correct answer:

a physical change

Explanation:

In a chemical change, the chemical bonds in the molecules break. The atoms then link together to form new molecules. The types of molecules in matter before and after a chemical change are always different. For example, burning a piece of paper is a chemical change. As paper burns, paper molecules react with oxygen molecules in the air. This reaction breaks the chemical bonds in the molecules. The atoms then relink and form different molecules. For example, carbon dioxide molecules are created when paper burns. Also, once a paper burns you can't get the original piece of paper back. When something can't go back to the original state (or object) this likely means a chemical change has occurred.

In a physical change, chemical bonds do not break. The types of molecules in matter before and after a physical change are always the same. A change of state is a type of physical change. For example, ice melting is a physical change. Ice and water are made of the same thing: water. You can also re-freeze melted water back to ice. When something can go back to the original state (or object) this likely means a physical change has occurred.

The answer is "a physical change" because the chemical composition of Zinc Chloride does not change as its melting.

Example Question #2 : Determine Whether A Chemical Reaction Has Occurred

A block of ice melting into a puddle of water is an example of:

Possible Answers:

a physical change

a chemical change

neither a physical nor a chemical change

both a physical and a chemical change

Correct answer:

a physical change

Explanation:

In a chemical change, the chemical bonds in the molecules break. The atoms then link together to form new molecules. The types of molecules in matter before and after a chemical change are always different. For example, burning a piece of paper is a chemical change. As paper burns, paper molecules react with oxygen molecules in the air. This reaction breaks the chemical bonds in the molecules. The atoms then relink and form different molecules. For example, carbon dioxide molecules are created when paper burns. Also, once a paper burns you can't get the original piece of paper back. When something can't go back to the original state (or object) this likely means a chemical change has occurred.

In a physical change, chemical bonds do not break. The types of molecules in matter before and after a physical change are always the same. A change of state is a type of physical change. For example, ice melting is a physical change. Ice and water are made of the same thing: water. You can also re-freeze melted water back to ice. When something can go back to the original state (or object) this likely means a physical change has occurred.

The answer is a physical change because ice and water are chemically identical and only the physical state changes when ice is melted to water.

Example Question #3 : Determine Whether A Chemical Reaction Has Occurred

Hydrochloric acid breaking down food during digestion is an example of:

Possible Answers:

luster

combustion

a chemical change

a physical change

Correct answer:

a chemical change

Explanation:

In a chemical change, the chemical bonds in the molecules break. The atoms then link together to form new molecules. The types of molecules in matter before and after a chemical change are always different. For example, burning a piece of paper is a chemical change. As paper burns, paper molecules react with oxygen molecules in the air. This reaction breaks the chemical bonds in the molecules. The atoms then relink and form different molecules. For example, carbon dioxide molecules are created when paper burns. Also, once a paper burns you can't get the original piece of paper back. When something can't go back to the original state (or object) this likely means a chemical change has occurred.

In a physical change, chemical bonds do not break. The types of molecules in matter before and after a physical change are always the same. A change of state is a type of physical change. For example, ice melting is a physical change. Ice and water are made of the same thing: water. You can also re-freeze melted water back to ice. When something can go back to the original state (or object) this likely means a physical change has occurred.

Combustion is the process of burning something. Which, as stated above, is a chemical reaction.

Luster is the way light interacts with the surface of a crystal, rock, or mineral. Luster is how shiny an object looks.

The answer is a chemical change because the "breaking down" of food is a chemical reaction.

Example Question #4 : Determine Whether A Chemical Reaction Has Occurred

Which of these is NOT an example of a chemical reaction?

Possible Answers:

plants undergoing photosynthesis

lighting a match

washing your hands with soap

iron being filed down and turned into powder

Correct answer:

iron being filed down and turned into powder

Explanation:

In a chemical change, the chemical bonds in the molecules break. The atoms then link together to form new molecules. The types of molecules in matter before and after a chemical change are always different. For example, burning a piece of paper is a chemical change. As paper burns, paper molecules react with oxygen molecules in the air. This reaction breaks the chemical bonds in the molecules. The atoms then relink and form different molecules. For example, carbon dioxide molecules are created when paper burns. Also, once a paper burns you can't get the original piece of paper back. When something can't go back to the original state (or object) this likely means a chemical change has occurred.

The answer is "iron being filed down to a powder" because the metal is undergoing a physical change and its chemical identity stays the same.

Example Question #5 : Determine Whether A Chemical Reaction Has Occurred

Cooking uses heat to cause chemical changes in food. For example, when you hard boil an egg, the hydrogen sulfide produced by heating the egg white can react with iron from the egg yolk to form a green ring around the yolk. How do you know a chemical reaction has occurred during this process?

Possible Answers:

the green ring around the yolk

you can smell the sulphur from the egg as gas is produced

You used heat to boil the water and the egg

All choices are correct

Correct answer:

All choices are correct

Explanation:

In a chemical change, the chemical bonds in the molecules break. The atoms then link together to form new molecules. The types of molecules in matter before and after a chemical change are always different. For example, burning a piece of paper is a chemical change. As paper burns, paper molecules react with oxygen molecules in the air. This reaction breaks the chemical bonds in the molecules. The atoms then relink and form different molecules. For example, carbon dioxide molecules are created when paper burns. Also, once a paper burns you can't get the original piece of paper back. When something can't go back to the original state (or object) this likely means a chemical change has occurred.

The answer is all of these, because color changes, heating, and production of gases are all signs of a chemical change.

Example Question #4 : Determine Whether A Chemical Reaction Has Occurred

Which of these is NOT a sign of a chemical reaction?

Possible Answers:

energy is absorbed or released

a change in color

a change in phase of matter

formation of a precipitate

Correct answer:

a change in phase of matter

Explanation:

In a chemical change, the chemical bonds in the molecules break. The atoms then link together to form new molecules. The types of molecules in matter before and after a chemical change are always different. For example, burning a piece of paper is a chemical change. As paper burns, paper molecules react with oxygen molecules in the air. This reaction breaks the chemical bonds in the molecules. The atoms then relink and form different molecules. For example, carbon dioxide molecules are created when paper burns. Also, once a paper burns you can't get the original piece of paper back. When something can't go back to the original state (or object) this likely means a chemical change has occurred.

In a physical change, chemical bonds do not break. The types of molecules in matter before and after a physical change are always the same. A change of state is a type of physical change. For example, ice melting is a physical change. Ice and water are made of the same thing: water. You can also re-freeze melted water back to ice. When something can go back to the original state (or object) this likely means a physical change has occurred.

The answer is "a change in the phase of matter" because state changes are examples of physical changes.

Example Question #7 : Determine Whether A Chemical Reaction Has Occurred

You are doing a science experiment in your classroom. Your teacher gives you these instructions and tells you a chemical reaction will take place.

Materials: ammonium nitrate (NH4NO3), tap water(H2O), Ziploc bags, a graduated cylinder and a balance.

Procedure:

1. Measure out 5 grams of ammonium nitrate and place it directly into a Ziploc plastic bag.

2. Using a graduated cylinder, measure exactly 10 mL of water .

3. Quickly, pour the water into the bag of ammonium nitrate, remove excess air and seal the bag.

4. Gently squeeze the bag to mix the solid and water. Observe while holding the bag.

After doing the experiment you recorded the following observations:

the water did not change color
the ammonium nitrate dissolved completely
the bag got much colder
no bubbles were produced

Which of these is a sign that a chemical reaction took place when you mix the ammonium nitrate and the water?

Possible Answers:

no bubbles were produced

the water did not change color

the ammonium nitrate dissolved completely

the bag got much colder

Correct answer:

the bag got much colder

Explanation:

In a chemical change, the chemical bonds in the molecules break. The atoms then link together to form new molecules. The types of molecules in matter before and after a chemical change are always different. For example, burning a piece of paper is a chemical change. As paper burns, paper molecules react with oxygen molecules in the air. This reaction breaks the chemical bonds in the molecules. The atoms then relink and form different molecules. For example, carbon dioxide molecules are created when paper burns. Also, once a paper burns you can't get the original piece of paper back. When something can't go back to the original state (or object) this likely means a chemical change has occurred.

The answer is "the bag got much colder" because the absorption of thermal energy is evidence that an endothermic reaction has occurred.

Example Question #5 : Determine Whether A Chemical Reaction Has Occurred

The difference between a chemical change and a physical change is:

Possible Answers:

A physical change does not change the chemical identity of a substance

only chemical reactions involve heat

only chemical reactions involve state changes

a chemical reaction changes the shape of a substance

Correct answer:

A physical change does not change the chemical identity of a substance

Explanation:

In a chemical change, the chemical bonds in the molecules break. The atoms then link together to form new molecules. The types of molecules in matter before and after a chemical change are always different. For example, burning a piece of paper is a chemical change. As paper burns, paper molecules react with oxygen molecules in the air. This reaction breaks the chemical bonds in the molecules. The atoms then relink and form different molecules. For example, carbon dioxide molecules are created when paper burns. Also, once a paper burns you can't get the original piece of paper back. When something can't go back to the original state (or object) this likely means a chemical change has occurred.

In a physical change, chemical bonds do not break. The types of molecules in matter before and after a physical change are always the same. A change of state is a type of physical change. For example, ice melting is a physical change. Ice and water are made of the same thing: water. You can also re-freeze melted water back to ice. When something can go back to the original state (or object) this likely means a physical change has occurred.

The answer is "a physical change does not change the chemical identity of a substance." Both chemical and physical changes can involve heat, change the shape of a substance, or involve state changes.

Example Question #6 : Determine Whether A Chemical Reaction Has Occurred

An "indicator" is a substance that changes color to tell us whether another chemical is present in our solution. An example of an indicator is the substance called "methyl yellow" which makes a yellow color in the presence of an alkaline. Indicators changing color are a sign that what has occurred?

Possible Answers:

both a physical and a chemical change

a physical change

a chemical change

neither a physical nor a chemical change

Correct answer:

a chemical change

Explanation:

In a chemical change, the chemical bonds in the molecules break. The atoms then link together to form new molecules. The types of molecules in matter before and after a chemical change are always different. For example, burning a piece of paper is a chemical change. As paper burns, paper molecules react with oxygen molecules in the air. This reaction breaks the chemical bonds in the molecules. The atoms then relink and form different molecules. For example, carbon dioxide molecules are created when paper burns. Also, once a paper burns you can't get the original piece of paper back. When something can't go back to the original state (or object) this likely means a chemical change has occurred.

In a physical change, chemical bonds do not break. The types of molecules in matter before and after a physical change are always the same. A change of state is a type of physical change. For example, ice melting is a physical change. Ice and water are made of the same thing: water. You can also re-freeze melted water back to ice. When something can go back to the original state (or object) this likely means a physical change has occurred.

The answer is a chemical change because indicators produce a color change.

Example Question #7 : Determine Whether A Chemical Reaction Has Occurred

The following equation represents what happens when you combine Hydrogen Chloride and Potassium Hydroxide: HCl + KOH → KCl + H2O. This is an example of:

Possible Answers:

a physical change because there is a state change

a chemical change because of the law of conservation of mass

a physical change because there is no new substance produced

a chemical change because a new substance is produced

Correct answer:

a chemical change because a new substance is produced

Explanation:

In a chemical change, the chemical bonds in the molecules break. The atoms then link together to form new molecules. The types of molecules in matter before and after a chemical change are always different. For example, burning a piece of paper is a chemical change. As paper burns, paper molecules react with oxygen molecules in the air. This reaction breaks the chemical bonds in the molecules. The atoms then relink and form different molecules. For example, carbon dioxide molecules are created when paper burns. Also, once a paper burns you can't get the original piece of paper back. When something can't go back to the original state (or object) this likely means a chemical change has occurred.

In a physical change, chemical bonds do not break. The types of molecules in matter before and after a physical change are always the same. A change of state is a type of physical change. For example, ice melting is a physical change. Ice and water are made of the same thing: water. You can also re-freeze melted water back to ice. When something can go back to the original state (or object) this likely means a physical change has occurred.

The answer is "a chemical change because a new substance is produced." The answer is not physical change and the reason is "because a new substance is produced" since we know a change in chemical identity occurs and the substance KCl is present on the other side of the equation. The law of conservation of mass is true of physical changes as well.

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Middle School Physical Science : Determine whether a chemical reaction has occurred

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Example Question #1 : Determine Whether A Chemical Reaction Has Occurred

Example Question #2 : Determine Whether A Chemical Reaction Has Occurred

Example Question #3 : Determine Whether A Chemical Reaction Has Occurred

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Example Question #4 : Determine Whether A Chemical Reaction Has Occurred

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