Unit 10 Review

What is the enthalpy change when 2 mol of CaO reacts completely with water?

• -127 kJ

• +127 kJ

• -63.5 kJ

• +63.5 kJ

Which thermochemical equation is the most correct equivalent to the chemical reaction and enthalpy given?

• CaO (s) + H2O (l) - 65.3kJ → Ca(OH)2

• CaO (s) + H2O (l) - 65.3kJ → Ca(OH)2

• CaO (s) + H2O (l) + 65.3kJ → Ca(OH)2

• CaO (s) + H2O (l) → Ca(OH)2 + 65.3kJ

Which of the following can be concluded from this thermochemical equation?

• The products of this reaction have more potential energy than the reactants.

• The formation of calcium hydroxide is an endothermic process.

• The total bond energies associated with forming bonds is greater than the total bond energies associated with breaking bonds.

• 63.5 kJ of heat must be absorbed from the surroundings for every 1 mole of calcium hydroxide formed.

A certain amount of 15.75 kJ of heat is needed to increase the temperature of 150.0g of a liquid hydrocarbon from 25.0°C to 55.0°C. Calculate the specific heat capacity of this hydrocarbon using the appropriate formula.

• 1.26 J/g°C

• 0.84 J/g°C

• 2.10 J/g°C

• 3.15 J/g°C

What occurs energetically when solid A, at 100.0°C, is placed in liquid B, at 80.0°C?

• Heat energy flows from A to B as the average kinetic energy of the particles in solid A decreases.

• Heat energy flows from A to B as the average kinetic energy of the particles in solid A increases.

• Heat energy flows from B to A as the average kinetic energy of the particles in liquid B increases.

• Heat energy flows from B to A as the average kinetic energy of the particles in liquid B decreases.

Which of the following changes to a chemical system would increase the rate of a reaction?

• Place the reaction vessel in a cooler

• Use large chunks of solid reactant instead of fine powder.

• Change the concentration of the reactants from 0.1 M to 1 M.

• Decrease the catalyst concentration

Calculate the ΔH_rxn in units of kJ/mol given the table of bond energies for the reaction: Br2 (g) + 3 F2 (g) → 2 BrF3 (g).

• -516 kJ/mol

• -410 kJ/mol

• -611 kJ/mol

• -720 kJ/mol

Ice cubes are placed in a glass of water that is at room temperature. Which statement BEST describes the temperature of the water after 10 minutes?

• The temperature decreases because some of the water's heat is lost to the ice.

• The temperature increases because some of the coolness of the water is absorbed by the ice.

• The temperature decreases because some of the ice's heat is lost to the water.

• The temperature increases because some of the coolness of the ice is absorbed by the water.

Which of the following is TRUE with respect to the collision theory of chemical reactions?

• Every collision of reactant molecules in a reaction vessel creates a product.

• Reactions that occur at a faster rate overall have a higher proportion of effective collisions.

• Reactions that occur at a slower rate have a lower proportion of ineffective collisions.

• A catalyst increases the proportion of ineffective collisions to increase the rate of reaction.

The graph shows a typical energy distribution for particles of an ideal gas in a sealed container at a fixed temperature. Which of the following statements is TRUE?

• The area under the curve to the right of E_a represents the number of molecules with enough energy to react.

• The area under the curve to the left of E_a represents the number of molecules with enough energy to react.

• Adding a catalyst to the reaction would shift E_a to the right.

• Adding a catalyst to the reaction would lower the height of the peak and shift the peak right.