AP Chem Unit 6

Which of the following can be concluded?

• D) The final temperature is less than the average starting temperature of the metal and the water; therefore the total energy of the metal and water decreased.

• A) The metal temperature changed more than the water temperature did; therefore the metal lost more thermal energy than the water gained.

• B) The metal temperature changed more than the water temperature did, but the metal lost the same amount of thermal energy as the water gained.

• C) The metal temperature changed more than the water temperature did; therefore the heat capacity of the metal must be greater than the heat capacity of the water

Answer explanation

According to the information above, what is the standard enthalpy of formation, ΔH°f , for NH₃(g) at 298 K ?

• C) 46 kJ/mol

• D) 92 kJ/mol

• A) -92 kJ/mol

• B) -46 kJ/mol

Answer explanation

• D) +244 kJ/mol_rxn

• A) -244 kJ/mol_rxn

• C) +183 kJ/mol_rxn

• B) -183 kJ/mol_rxn

Answer explanation

Which of the following best explains why the enthalpy of vaporization of methane is less than that of water?

• D) Methane has a much lower density.

• A) Methane does not exhibit hydrogen bonding, but water does.

• B) Methane has weaker dispersion forces.

• C) Methane has a smaller molar mass.

Answer explanation

The graph shows the temperature of a pure substance as it is heated at a constant rate in an open vessel at 1.0 atm pressure. The substance changes from the solid to the liquid to the gas phase.

The substance is at its normal freezing point at time :

• A) t₁

• C) t₃

• B) t₂

• D) t₄

Answer explanation

On the basis of the information, which of the following is the enthalpy of decomposition of 2 mol of H₂O₂ (l)?

• D) +349 kJ

• A) -349 kJ

• C) +203 kJ

• B) -203 kJ

Answer explanation

Based on the reaction represented by the chemical equation shown above, what is the amount of heat released when 4.00mol of H₂S(g) reacts with 9.00mol of O₂(g)?

• C) -2240 kJ

• A) -560 kJ

• D) -3360 kJ

• B) -1120 kJ

Answer explanation

Based on the information above, what is the enthalpy change for the sublimation of iodine, represented below?

• A) 15 kJ/mol

• B) 21 kJ/mol

• C) 31 kJ/mol

• D) 42 kJ/mol

• E) 62 kJ/mol

Answer explanation

• D) +773 kJ

• A) -607 kJ

• C) +19 kJ

• B) -147 kJ

Answer explanation

Which of the following best identifies the change in enthalpy in the phase transition shown in the diagram?

• D) -77.2 kJ

• A) +19.3 kJ

• C) -19.3 kJ

• B) +77.2 kJ

Answer explanation