Balancing Chemical Equations

Students are conducting an experiment to find out what they can do to make a reaction between hydrochloric acid (HCl) and magnesium (Mg) follow the Law of Conservation of Mass. The data from their experiment is in the chart shown. Which idea would improve the design of the experiment so that the results would more accurately demonstrate the Law of Conservation of Mass?

• Students should put a balloon over the top of the flask to close the system.

• Students should add more magnesium to the reaction to increase the mass of the products.

• Students should decrease the amount of acid to decrease the mass of the products.

• Students should add ice to the reaction to stop the reaction from boiling the acid away.

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7-PS1-5

How does the concept of the Law of the Conservation of Mass apply to chemical reactions?

• The reactants and products have exactly the same molecules.

• The change in the amount of matter is equal to the change in energy.

• The reactants and products have exactly the same atoms.

• The change in the amount of matter is only a small percentage of the total mass.

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7-PS1-5

The picture shows steps in the reaction of fireworks burning. Which statement about the reaction is true?

• Matter was destroyed, leaving fewer atoms at the end of the reaction.

• New matter was created in the form of light and heat during the reaction.

• Atoms were destroyed leaving lower-energy atoms in the products of the reaction.

• Atoms were rearranged, but no matter was created or destroyed in the reaction.

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NGSS.MS-PS1-2

NGSS.MS-PS1-5

What does the arrow represent in a chemical equation?

• breaks apart

• yields

• combines

• chemically reacts

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NGSS.MS-PS1-2

The equation for cellular respiration is shown. According to the reaction, what are the products of cellular respiration?

• glucose and oxygen

• sugar and oxygen

• sugar and energy

• carbon dioxide, water, and energy

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7-PS1-5

A balanced chemical equation is shown in the image. How many total atoms are found on each side of the arrow?

• 2

• 4

• 6

• 8

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NGSS.MS-PS1-1

NGSS.MS-PS1-5

Why is it important to balance chemical equations?

• Balanced equations represent the physical changes that take place when 2 substances combine as a mixture.

• Balanced equations follow the Law of Conservation of Matter which represents what actually happens in nature.

• Balanced equations prove that matter is either created or destroyed during a chemical reaction by showing all the atoms.

• Balanced equations show that the mass of the products is always less than the mass of the reactants because mass is lost as heat.

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7-PS1-5

The chemical formula for nitric acid is HNO₃. What composes this compound?

• 1 helium atom, 1 nitrogen atom, and 3 osmium

• 1 hydrogen atom, 1 sodium atom, and 3 oxygen atoms

• 1 helium atom, 1 sodium atom, and 3 osmium atoms

• 1 hydrogen atom, 1 nitrogen atom, and 3 oxygen atoms

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7-PS1-5

Which equation is correctly balanced for hydrogen and oxygen reacting to form water?

• H₂ + O₂ --> H₂O

• 2H₂ + O₂ --> 2H₂O

• 4H + O₂ --> 2H₂O

• H₂ + O --> H₂O

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7-PS1-5

Which represents the reactants of the chemical equation?

• CH₄ and O₂

• CO₂ and H₂O

• CH₄ and CO₂

• O₂ and H₂O

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7-PS1-5