Stoichiometric calculations involving energy terms: Practice Questions

The standard enthalpy of neutralization for the reaction between a strong acid and a strong alkali is $$-57.3\thinspace\text{kJ mol}^{-1}$$. If $$0.25\thinspace\text{mol}$$ of hydrochloric acid is completely neutralized by an excess of sodium hydroxide solution, what is the heat released?

A solid substance X has a molar mass of $$50.0 \text{ g mol}^{-1}$$. When $$2.50 \text{ g}$$ of X is dissolved in $$100.0 \text{ cm}^3$$ of water, the temperature of the resulting solution decreases from $$25.0^\circ\text{C}$$ to $$23.5^\circ\text{C}$$. Assume the specific heat capacity of the solution is $$4.18 \text{ J g}^{-1} \text{ K}^{-1}$$ and its density is $$1.00 \text{ g cm}^{-3}$$. Neglect the heat capacity of the calorimeter. What is the molar enthalpy of solution of X?

A camping heater is designed to provide \( 1500 \text{ kJ} \) of heat energy to boil water. The heater burns liquid methanol (\( CH_3OH \)) as fuel. If the heating process is only \( 80.0\% \) efficient, what mass of methanol must be burned to provide the required energy?

(Given: \( \Delta H_f^\circ [CH_3OH(l)] = -239.1 \text{ kJ mol}^{-1} \); \( \Delta H_f^\circ [CO_2(g)] = -393.5 \text{ kJ mol}^{-1} \); \( \Delta H_f^\circ [H_2O(l)] = -285.8 \text{ kJ mol}^{-1} \); Molar mass of \( CH_3OH = 32.0 \text{ g mol}^{-1} \))

The standard enthalpy change of combustion of methane (\( \text{CH}_4 \)) is \( -890\thinspace\text{kJ mol}^{-1} \). What is the heat released when \( 3.2\thinspace\text{g} \) of methane is completely burnt in excess oxygen?
(Relative atomic masses: \( \text{H} = 1.0, \text{C} = 12.0 \))

Given the standard enthalpy changes of combustion (\( \text{Δ}H_\text{c}^\text{o} \)) at \( 298 \text{ K} \) for the following substances:
\( \text{C(graphite)} = -393.5 \text{ kJ mol}^{-1} \)
\( \text{H}_2\text{(g)} = -285.8 \text{ kJ mol}^{-1} \)
\( \text{C}_6\text{H}_6\text{(l)} = -3267.0 \text{ kJ mol}^{-1} \)

What is the standard enthalpy change of formation (\( \text{Δ}H_\text{f}^\text{o} \)) of liquid benzene (\( \text{C}_6\text{H}_6 \))?

When \(0.5\) mole of a substance undergoes a reaction that releases \(250 \text{ kJ}\) of heat energy, what is the molar enthalpy change for this reaction?

When \( 0.40 \, \mathrm{g} \) of methane (\( \mathrm{CH}_4 \)) is completely burnt in excess oxygen, \( 22.3 \, \mathrm{kJ} \) of heat is released. Calculate the molar enthalpy change of combustion of methane in \( \mathrm{kJ \, mol}^{-1} \).
(Relative atomic masses: \( \mathrm{C} = 12.0, \mathrm{H} = 1.0 \))

A student used a simple calorimeter to burn \( 0.60\thinspace\text{g} \) of propan-1-ol (\( \text{C}_3\text{H}_7\text{OH} \)) to heat \( 200.0\thinspace\text{g} \) of water. The water temperature increased by \( 18.0\thinspace\text{K} \). If the theoretical enthalpy of combustion of propan-1-ol is \( -2021\thinspace\text{kJ mol}^{-1} \), calculate the percentage of heat energy lost to the surroundings.
(Specific heat capacity of water = \( 4.18\thinspace\text{J g}^{-1}\text{ K}^{-1} \); Molar mass of propan-1-ol = \( 60.0\thinspace\text{g mol}^{-1} \))

A student performed an experiment to determine the temperature change of water when a small amount of ethanol (\(C_2H_5OH\)) is burnt. The standard enthalpy change of combustion of ethanol is \(-1367\thinspace\text{kJ mol}^{-1}\). In the experiment, \(0.46\thinspace\text{g}\) of ethanol was completely burnt and all the heat produced was assumed to be transferred to \(100.0\thinspace\text{g}\) of water.

a) Calculate the number of moles of ethanol burnt.
(Relative atomic masses: \(H = 1.0, C = 12.0, O = 16.0\))

b) Calculate the theoretical amount of heat energy released (in kJ) by the ethanol.

c) Calculate the theoretical temperature rise of the water in \(^{\circ}\text{C}\).
(Specific heat capacity of water = \(4.18\thinspace\text{J g}^{-1}\text{ K}^{-1}\))

A student conducted an experiment to determine the average carbon-carbon double bond (C=C) enthalpy in ethene (\(C_2H_4\)) using a simple calorimeter.

Experiment:

0.50 g of gaseous ethene was completely combusted. The heat released was used to warm 100.0 g of water in a copper calorimeter. The initial temperature of the water was \(25.0^\circ\text{C}\), and the final temperature after combustion was \(73.6^\circ\text{C}\).

Given data:

• Specific heat capacity of water = \(4.18 \text{ J g}^{-1} \text{ K}^{-1}\)
• Heat capacity of copper calorimeter = \(100 \text{ J K}^{-1}\)
• Molar mass of ethene (\(C_2H_4\)) = \(28.0 \text{ g mol}^{-1}\)
• Standard enthalpy of formation of carbon dioxide, \(\Delta H_f^\circ [\text{CO}_2\text{(g)}] = -393.5 \text{ kJ mol}^{-1}\)
• Standard enthalpy of formation of liquid water, \(\Delta H_f^\circ [\text{H}_2\text{O(l)}] = -285.8 \text{ kJ mol}^{-1}\)
• Standard enthalpy of atomisation of carbon (graphite), \(\Delta H_{atom}^\circ [\text{C(s)}] = +715.0 \text{ kJ mol}^{-1}\)
• Average bond enthalpy of H-H, \(E(\text{H-H}) = +436.0 \text{ kJ mol}^{-1}\)
• Average bond enthalpy of C-H, \(E(\text{C-H}) = +413.0 \text{ kJ mol}^{-1}\)

(a) Calculate the experimental standard enthalpy of combustion of ethene (\(\Delta H_c^\circ [\text{C}_2\text{H}_4\text{(g)}]\)) in \(\text{kJ mol}^{-1}\).

(b) Using your answer from (a) and relevant given standard enthalpy of formation values, calculate the standard enthalpy of formation of gaseous ethene (\(\Delta H_f^\circ [\text{C}_2\text{H}_4\text{(g)}]\)) in \(\text{kJ mol}^{-1}\). You should show an appropriate energy cycle or equations manipulated according to Hess's Law.

(c) Using your answer from (b) and relevant given bond enthalpy and atomisation values, calculate the average C=C bond enthalpy in ethene in \(\text{kJ mol}^{-1}\). You should show an appropriate energy cycle or equations manipulated according to Hess's Law.