07.00 Energy in Reactions

Which statement is true about the potential energy diagram for an exothermic reaction?

• Energy value remains the same throughout the diagram.

• Products have more potential energy than reactants.

• Potential energy of the products is equal to the potential energy of the reactants.

• It starts at a higher energy value and ends at a lower energy value.

The graph shows the potential energy diagram for an unknown chemical change.Which chemical change could the graph represent? (1 point)

• Adding heat to decompose calcium carbonate

• Photosynthesis in plants

• Combustion of iron

• Electrolysis of water

Which of the following is a characteristic of an endothermic chemical reaction? (1 point)

• The energy of the reactants is higher than the energy of the products.

• The amount of energy released is equal to the activation energy.

• Energy is released into the surroundings during this change.

• The overall enthalpy of the system increases during the change.

Four substances at the same temperature absorb equal amounts of energy. The specific heats of the four substances are 1.01 J/g °C, 1.01 J/g °C, 0.38 J/g °C, and 0.44 J/g °C. What is the specific heat value of the substance that will have highest increase in temperature? (1 point)

• 0.84 J/g °C

• 1.01 J/g °C

• 0.38 J/g °C

• 0.44 J/g °C

How many joules are absorbed when 64.3 grams of water is heated from 40.0 °C to 74.0 °C? (1 point)

• 7,330 joules

• 9,150 joules

• 10,100 joules

• 12,800 joules

During a reaction, ΔH for reactants is −750 kJ/mol and ΔH for products is 920 kJ/mol. Which statement is correct about the reaction? (1 point)

• It is endothermic because the energy required to break bonds in the reactants is less than the energy released when the products are formed.

• It is endothermic because the energy required to break bonds in the reactants is greater than the energy released when the products are formed.

• It is exothermic because the energy required to break bonds in the reactants is less than the energy released when the products are formed.

• It is exothermic because the energy required to break bonds in the reactants is greater than the energy released when the products are formed.

Which statement is correct about the rate of a chemical reaction? (1 point)

• It increases when the concentration of reactants increases.

• It does not depend on the concentration of reactants.

• It increases when the temperature decreases.

• It does not depend on the temperature.

The volume of a reaction vessel with gaseous reactants is lowered to one-fourth of its original volume. What will happen to the rate of the reaction? (1 point)

• It will increase because the concentration of the reactants increases.

• It will decrease because the concentration of the reactants decreases.

• It will increase because the gaseous particles are moved farther apart.

• It will decrease because the gaseous particles are brought closer together.

Which of the following happens when a reaction reaches dynamic equilibrium in a closed system? (1 point)

• The concentrations of the reactants and products increase.

• The concentration of the reactants and products remain constant.

• The rate of the forward reaction is faster than the rate of the reverse reaction.

• The rate of the forward reaction is slower than the rate of the reverse reaction.

The equilibrium constant K for a certain reversible reaction is 1.32 × 10⁻⁴. Which of the following is true for the reaction? (1 point)

• The reverse reaction is more favorable than the forward reaction.

• The forward reaction takes place at a much faster rate than the reverse reaction.

• The equilibrium reaction mixture will have a very low concentration of reactants.

• The equilibrium reaction mixture will have a very high concentration of products.