Chemical Reactions Unit Review

After reading about the kinds of changes that occur, Liz saw some rust on a pipe that was going into her house. What kind of change is the formation of rust?

• reactant

• chemical

• physical

• evaporation

Answer explanation

The formation of rust is a chemical change. It involves a chemical reaction between iron, oxygen, and water.

Tags

NGSS.MS-PS1-5

After learning about chemical reactions, Olivia investigated different kinds of chemical changes using substances she found in her kitchen so she could see these changes. Which of the following can occur when a chemical reaction takes place? (CHOOSE ALL THAT APPLY)

• New bonds form.

• Existing bonds break.

• New substances form.

• Changes don’t affect matter.

Answer explanation

During a chemical reaction, new bonds form, existing bonds break, and new substances are formed.

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NGSS.MS-PS1-2

NGSS.MS-PS1-5

Kim understands that there are several signs that indicate a chemical

reaction has occurred. What is the best way to be certain that a

chemical reaction has occurred?

• Some bubbles form.

• A color change occurs.

• The taste changes

• A new substance forms

Answer explanation

The best way to be certain that a chemical reaction has occurred is when a new substance forms.

Tags

NGSS.MS-PS1-2

Liz and Kyle are performing an experiment. They have been told by their teacher that in order for the reaction to occur there must be enough activation energy. What is activation energy in this context?

• The minimum amount of energy needed for the reaction to start.

• The amount of energy destroyed during the reaction

• The amount of energy created during the reaction

• The maximum amount of energy needed for the reaction to start.

Answer explanation

Activation energy is the minimum amount of energy needed for the reaction to start.

The rate of a chemical reaction is affected by which of the following:

• temperature

• concentration

• particle size (surface area)

• All of these affect reaction rates

Answer explanation

The rate of a chemical reaction is affected by temperature, concentration, and particle size (surface area). All of these factors affect reaction rates.

Tags

NGSS.HS-PS1-5

Michael wants to make a chemical reaction go faster. What could he do to make this happen? (choose all that apply)

• Increase the temperature

• decrease the temperature

• increase the surface area of the reactants

• decrease the surface area of the reactants

Answer explanation

Increasing the temperature and increasing the surface area of the reactants can make a chemical reaction go faster.

Tags

NGSS.HS-PS1-5

To lower the activation energy of a reaction and make it start faster, a (an) _______ could be used.

• exothermic

• endothermic

• Catalyst

• Materialist

Answer explanation

A catalyst can lower the activation energy of a reaction, making it start faster.

When we performed an experiment of making chalk and vinegar react. We ensured to crush the chalk thoroughly first. Why was that step important?

• Because it decreased surface area which increased the rate of reaction.

• Because it increased surface area which increased the rate of reaction.

• Because it decreased surface area which decreased the rate of reaction.

Answer explanation

Crushing the chalk increased its surface area, which accelerated the reaction rate.

What kind of reaction is this:
2H₂O₂ →2 H₂O + O₂

• Synthesis

• Decomposition

• Single Replacement 

• Combustion

Answer explanation

This reaction is a decomposition reaction because a single compound, H2O2, breaks down into two simpler substances, H2O and O2.

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NGSS.MS-PS1-2

NGSS.MS-PS1-5

Which of the following are PRODUCTS?
H₂O + CO₂ → HCO + HO

• H₂O and CO₂

• HCO and HO

• H₂O ONLY

• HCO ONLY

Answer explanation

The correct products in the reaction are HCO and HO. They are formed by the combination of H2O and CO2.

Tags

NGSS.MS-PS1-1

NGSS.MS-PS1-2