Energetics: Practice Questions

In an exothermic reaction, which of the following statements regarding the enthalpy level diagram is correct?

Which of the following equations correctly represents the standard enthalpy change of formation, \(\Delta_f H^{\ominus}\), for liquid water?

50.0 cm³ of \(1.00 \text{ mol dm}^{-3}\) HCl is reacted with 50.0 cm³ of \(1.00 \text{ mol dm}^{-3}\) NaOH in an insulated container. The temperature of the mixture rises by \(6.80 \text{ }^{\circ}\text{C}\). Calculate the energy transferred to the solution.
(Assume density of solution = \(1.00 \text{ g cm}^{-3}\), specific heat capacity \(c = 4.18 \text{ J g}^{-1} \text{ K}^{-1}\))

Which statement correctly describes an exothermic reaction?

Calculate the heat energy required to increase the temperature of a \(250 \text{ g}\) block of copper from \(20 \text{ }^{\circ}\text{C}\) to \(150 \text{ }^{\circ}\text{C}\).

(Specific heat capacity of copper = \(0.385 \text{ J g}^{-1} \text{ K}^{-1}\))

Define the term standard enthalpy change of formation, \(\Delta H_{\text{f}}^{\ominus}\).

Calculate the enthalpy change, \(\Delta H\), in \(\text{kJ mol}^{-1}\), when \(100 \text{ cm}^3\) of \(1.0 \text{ mol dm}^{-3} \text{ HCl}\) reacts with \(100 \text{ cm}^3\) of \(1.0 \text{ mol dm}^{-3} \text{ NaOH}\), causing a temperature rise of \(6.8 \text{ }^{\circ}\text{C}\). (Assume density = \(1.0 \text{ g cm}^{-3}\) and \(c = 4.18 \text{ J g}^{-1} \text{ K}^{-1}\)).

A student determines the enthalpy of combustion of methanol using a copper calorimeter. If heat loss to the surroundings occurs, explain the impact on the calculated temperature change and the final enthalpy value.

A student uses a simple calorimeter to determine the enthalpy of combustion of methanol, \(CH_3OH\). 0.80 g of methanol was burned, and the temperature of 100 g of water increased by 22.5 °C.
(a) Calculate the heat energy transferred to the water in kJ. (Specific heat capacity of water = 4.18 J g\(^{-1}\) °C\(^{-1}\))
(b) Calculate the molar enthalpy of combustion of methanol in kJ mol\(^{-1}\). (Molar mass of methanol = 32.0 g mol\(^{-1}\))

The standard enthalpy changes of combustion (\(\Delta H_c^{\ominus}\)) for graphite, hydrogen, and benzene are given below:
C(graphite) = -394 kJ mol\(^{-1}\)
H\(_2\)(g) = -286 kJ mol\(^{-1}\)
C\(_6\)H\(_6\)(l) = -3267 kJ mol\(^{-1}\)
(a) Write the equation for the standard enthalpy change of formation of benzene, \(C_6H_6(l)\).
(b) Construct a Hess cycle and calculate the standard enthalpy change of formation of benzene.