Chemistry Review Questions

1. Chemistry Review Questions Fe2O3 + 2 Al  2 Fe + Al2O3 + Energy

2. A friend argues that if mass were really conserved, he would never need to refill his gas tank. What explanation do you offer your friend? The Law of Conservation of Mass does not apply to reactions involving combustion of matter. The oil companies make gasoline in a way that it gets used up so that we are always required to replenish it. The nucleii of the atoms (mass) of gasoline are converted into pure energy by the engine according to E = mc2. The atoms (mass) of gasoline are rearranged and converted into exhaust fumes.

3. A refrigerator delays the spoilage of food by killing microorganisms. slowing the rate of chemical reactions within microorganisms. expanding the water found within microorganisms. diminishing the supply of oxygen to microorganisms.

4. Temperature

5. Why does wood burn slowly in air but rapidly bursts into flames when placed in pure oxygen? There is a greater interaction between the wood and oxygen molecules. Because oxygen can lower the activation energy of the reaction. Pure oxygen reacts with carbon dioxide at a faster rate. Fire is actually extinguished within pure oxygen.

6. Transformation of stored chemical energy to heat energy through combustion of plant material: Plant + O2 CO2 + H2O + C + Other Gases + Energy

7. Concentration

8. True or False? Catalysts increase the rate of a chemical reaction by increasing the activation energy required for a reaction to take place. • True • False

9. Catalysts Transformation of Ozone to Oxygen by Chlorine in atmosphere. Ea is reduced by Chlorine catalyst.

10. If a reaction container feels cooler after a reaction has occurred, the reaction was • Endothermic • Exothermic

11. Ultraviolet Sun rays within the stratosphere cause oxygen molecules (O2) to transform into ozone molecules (O3). Is this an example of an exothermic or an endothermic reaction? Exothermic, because ultraviolet light is emitted. Endothermic, because ultraviolet light is emitted. Exothermic, because ultraviolet light is absorbed. Endothermic, because ultraviolet light is absorbed. 3 O2 + UV  2 O3

12. Energy and Chemical Reactions Exothermic reaction: a chemical reaction that results in the net release of energy. reactants products + energy Endothermic reaction: a chemical reaction in which there is a net consumption of energy. energy + reactants products

13. How is it possible to cause an endothermic reaction to proceed when the reaction causes energy to be less dispersed? • The reaction should be placed in a vacuum. • The reaction should be cooled down. • The concentration of the reactants should be increased. • The reaction should be heated.

14. What type of reactions tend to occur all by themselves without the continuous input of energy? Exothermic reactions, because they increase entropy. Endothermic reactions, because they increase entropy. Exothermic reactions, because they decrease entropy. Endothermic reactions, because they decrease entropy.

15. Which of the following is true about the concept of bond energy in chemistry? • The minimum energy required to break a chemical bond. • The amount of energy released in forming a chemical bond. • Can determine if a chemical reaction is exothermic or endothermic. • All of the above.

16. Energy and Chemical Reactions • Bond Energy: • Energy absorbed in order to break a chemical bond = energy released when the same chemical bond is formed.

17. Look at the graph showing how chemical potential energy changes during a chemical reaction. What type of reaction is this? • Endothermic • Exothermic

18. Exothermic Reaction Energy absorbed in breaking chemical bonds in reactants < Energy released in forming chemical bonds in products Products have lower chemical potential energy than reactants. Energy released in reaction = difference in potential energies = difference in bond energies.