Evidence of Chemical Reactions

What is a chemical reaction?

• A chemical reaction is a change in state

• A chemical reaction is a biological process

• A chemical reaction is a physical change

• A chemical reaction is a process that leads to the transformation of one set of chemical substances to another.

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What are some common signs that a chemical reaction has occurred?

• Color change, gas production, formation of a precipitate, temperature change, and odor change.

• Change in volume

• Change in texture

• Formation of bubbles

• Change in pressure

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Explain the difference between physical and chemical changes.

• Physical changes involve a change in color, while chemical changes do not.

• Physical changes are reversible, while chemical changes are irreversible.

• Physical changes do not alter the chemical composition of a substance, while chemical changes result in the formation of new substances.

• Physical changes result in new substances, while chemical changes do not alter the chemical composition of a substance.

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Give an example of a chemical reaction that produces a gas.

• Iron + Sulfur -> Nitrogen gas

• Sugar + Lemon juice -> Hydrogen gas

• Salt + Water -> Oxygen gas

• Baking soda + Vinegar -> Carbon dioxide gas

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What is a precipitate and how does it indicate a chemical reaction?

• A precipitate is a liquid that forms when two solutions react chemically.

• A precipitate is a gas that forms when two solutions react chemically.

• A precipitate is a solid that forms when two solutions react chemically. It indicates a chemical reaction because the formation of a precipitate is evidence that a chemical change has occurred.

• A precipitate is a solution that forms when two solids react chemically.

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Why is it important to balance chemical equations?

• To make the equations longer

• To confuse students

• To waste time

• To ensure the law of conservation of mass is obeyed.

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What is the law of conservation of mass and how does it relate to chemical reactions?

• The law of conservation of mass is only relevant in physics, not chemistry

• The law of conservation of mass states that mass can be created or destroyed in chemical reactions

• The law of conservation of mass is a fundamental principle in chemistry that states mass is conserved in chemical reactions.

• The law of conservation of mass only applies to solid substances

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Four students performed four different investigations by combining different substances. Their results are shown in the table provided. In which experiment are new substances being formed?

• Experiment 1
• Experiment 2
• Experiment 3
• Experiment 4

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Evidence of a chemical reactions is anything that shows - 

• a new substance has formed
• a solid dissolved in a liquid
• interaction between 2 gases
• a change in the state of matter

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What is the Law of Conservation of mass?

• Mass is created in a chemical reaction
• Mass is created in a physical change
• New chemicals formed from a chemical reaction have a larger overall mass than the original reactants
• Mass is never created or destroyed

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