Which of the following is the correct definition of formation enthalpy?

A. The enthalpy change when one mole of a compound is formed from its elements in their standard states.

B. The enthalpy change when one mole of a compound is burned completely in oxygen.

C. The enthalpy change when a solution is formed from a solute and a solvent.

D. The enthalpy change when an acid reacts with a base to form one mole of water.

What does combustion enthalpy refer to?

A. The energy required to break one mole of bonds in a compound.

B. The energy change when one mole of a compound is dissolved in water.

C. The energy change when one mole of a compound is burned completely in oxygen.

D. The energy change when an acid reacts with a base.

Which of the following best describes Hess's Law?

A. The total enthalpy change of a reaction is independent of the route taken.

B. The enthalpy change of a reaction is directly proportional to the amount of reactants used.

C. The enthalpy change of a reaction is always negative.

D. The enthalpy change of a reaction is equal to the sum of the enthalpies of the products minus the enthalpies of the reactants.

What is the significance of standard conditions when discussing enthalpy changes?

A. They refer to conditions at 0°C and 1 atm pressure.

B. They ensure that enthalpy changes are measured under consistent conditions for comparison.

C. They are the conditions under which all reactions occur.

D. They are the conditions at which a reaction is most spontaneous.

Which of the following reactions is likely to have a negative solution enthalpy?

A. A reaction in which a gas is produced.

B. A reaction in which a solid is formed from a solution.

C. A reaction in which a solution gets colder upon dissolving a solute.

D. A reaction in which a solution gets warmer upon dissolving a solute.

a) Define formation enthalpy and explain its significance in thermochemistry. [3]

b) Given that the formation enthalpy of water is -285.8 kJ/mol, determine the energy change when 2 moles of water are formed from its elements. [2]

a) Describe the concept of combustion enthalpy and how it differs from formation enthalpy. [3]

b) Why is the combustion enthalpy of methane always negative? [2]

a) Explain the principle behind Hess's Law and its applications in determining enthalpy changes. [3]

b) If the enthalpy change for the combustion of carbon to carbon dioxide is -393.5 kJ/mol and that of the combustion of hydrogen to water is -285.8 kJ/mol, calculate the enthalpy change for the combustion of methane (CH4). [2]

a) Discuss the concept of entropy and its relation to the disorder of a system. [3]

b) Calculate the change in entropy when 2 moles of a gas at 25°C and 1 atm pressure expand irreversibly from a volume of 5 L to 10 L. (Assume ideal behaviour) [4]

c) Explain how the change in entropy is related to the spontaneity of a process. [2]

a) Define standard conditions in thermochemistry and explain why they are important when calculating enthalpy changes. [3]

b) Calculate the enthalpy change for the combustion of 1 mole of benzene (C6H6) to form carbon dioxide and water vapour. Given: C6H6(l) + 15/2 O2(g) → 6 CO2(g) + 3 H2O(g) ΔH = -3267 kJ/mol [4]

c) Discuss the factors that can affect the magnitude of the entropy change in a chemical reaction. [3]