L7 Quiz Chemical Reactions and Energy

Which statement describes the role of energy in chemical reactions?

•  

  Energy is destroyed in endothermic reactions.

• Energy is always released in chemical reactions.

•  

  Energy is created in exothermic reactions.

• Energy is needed for chemical reactions to start.

Answer explanation

Energy is always required to start reactions. regardless of whether the reaction absorbs or releases energy overall. This is called activation energy.

According to the law of conservation of energy, which of the following is true?

•  

  Energy can be destroyed.

•  

  Energy can change form.

•  

  Energy can be created.

• Energy is not involved in chemical reactions.

Answer explanation

Energy can change form.

In a compound, where is the chemical energy contained?

•  

  movement of the electrons

•  

  bonds

• unbonded electrons

•  

  nuclei of the atoms

Answer explanation

Chemical energy is stored in the chemical bonds of a substance.

Which of the following is true about energy in chemical reactions?

•  

  Energy is not involved in chemical reactions.

• Energy is required to break bonds.

• Energy is required when bonds are formed.

•  

  Energy is released when bonds are broken.

Answer explanation

Energy is required to break bonds, which is required for reactions to happen.

Which letter in the image below represents the activation energy of the reaction?

• A

• B

• C

• D

Answer explanation

Letter B represents the activation energy.

In terms of energy, how would you classify the following chemical reaction?2Cu + O₂ → 2CuO + energy

• endothermic

• exothermic

•  

  both endothermic and exothermic

• neither endothermic nor exothermic

Which term describes a chemical reaction where the products have less chemical energy than reactants?

•  

  energetically stable

• isothermic

•  

  endothermic

• exothermic

Answer explanation

When the products are lower in energy than the reactants, the reaction is called exothermic.

What type of chemical reaction absorbs energy?

• endothermic

• both exothermic and synthesis

•  

  exothermic

• synthesis

Answer explanation

Energy is absorbed during an endothermic reaction.

What do you know to be true if you mix two room temperature solutions together and the temperature of the final solution decreases?

•  

  The chemical reaction is exothermic.

• The chemical reaction is releasing energy.

• Nothing happened in the chemical reaction.

• The chemical reaction is absorbing energy.

Answer explanation

When temperature decreases, that means that energy is being absorbed by the reaction. This is an endothermic reaction.

What is true when energy is listed as product of a chemical reaction?

• The energy is being used to break apart the reactants.

• The reaction uses a catalyst.

• The reaction is exothermic.

•  

  The reaction is endothermic.

Answer explanation

Energy as a product means that it is absorbed, so the reaction is endothermic.