Chemical Energetics

Define enthalpy change of formation.

Complete Table 4.1 by adding equations with relevant state symbols to represent:

• standard enthalpy change of formation for $\text{Fe}_2\text{O}_3$
• standard enthalpy change of formation for CO.

Use the data in Table 4.1 to calculate the enthalpy change of reaction, $\Delta H_r$, in $\text{kJ mol}^{-1}$, for reaction 2.

Show your working.

$\Delta H_r$ = .............................. $\text{kJ mol}^{-1}$

Explain the meaning of the term standard enthalpy change of combustion.

Write the equation for the complete combustion of ethanol, $\text{C}_2\text{H}_5\text{OH}$.

Calculate the heat energy change, $q$, during the combustion of $0.23\text{ g}$ of ethanol.

Calculate the enthalpy change on burning 1 mole of ethanol. Include a sign in your answer.

Suggest two reasons why the value for the enthalpy change of combustion of ethanol determined by a simple laboratory calorimetry experiment is likely to be lower than the true value.

Construct a labelled energy cycle to show how these values could be used to calculate the enthalpy change of formation of $\text{C}_3\text{H}_7\text{OH}(\text{l})$, $\Delta H_{\text{f}}$.

Calculate the enthalpy change of formation, $\Delta H_{\text{f}}$, of $\text{C}_3\text{H}_7\text{OH}(\text{l})$.

Explain the meaning of the term standard enthalpy change of combustion.

Write the equation for the complete combustion of ethanol, $\text{C}_2\text{H}_5\text{OH}$.

Calculate the heat energy change, $q$, during the combustion of $0.23\text{ g}$ of ethanol.

Calculate the enthalpy change on burning 1 mole of ethanol. Include a sign in your answer.

Suggest two reasons why the value for the enthalpy change of combustion of ethanol determined by a simple laboratory calorimetry experiment is likely to be lower than the true value.

Construct a labelled energy cycle to show how these values could be used to calculate the enthalpy change of formation of $\text{C}_3\text{H}_7\text{OH}(\text{l})$, $\Delta H_f$.

Calculate the enthalpy change of formation, $\Delta H_f$, of $\text{C}_3\text{H}_7\text{OH}(\text{l})$.

Propane and butane have different values of standard enthalpy change of combustion.

Define the term standard enthalpy change of combustion.

Use relevant data from the Data Booklet to calculate the amount of heat released in this experiment.

Use the data above and your answers to (i) and (ii) to calculate the energy produced by the burning of $1\text{ mol}$ of propane.

Propane and butane have different values of standard enthalpy change of combustion.

Define the term standard enthalpy change of combustion.

Use relevant data from the Data Booklet to calculate the amount of heat released in this experiment.

Use the data above and your answers to (i) and (ii) to calculate the energy produced by the burning of $1\text{ mol}$ of propane.

Define the term standard enthalpy change of combustion.

Use relevant data from the Data Booklet to calculate the amount of heat released in this experiment.

Use the data above and your answer to (i) to calculate the energy produced by the combustion of $1\text{ mol}$ of $\text{C}_{14}\text{H}_{30}$.

Define, with the aid of an equation which includes state symbols, the standard enthalpy change of combustion, $\Delta H_c^\ominus$, for DME at 298 K.

equation ....................................................................................................................

definition ...................................................................................................................

DME may be synthesised from methanol. Relevant enthalpy changes of formation, $\Delta H_f^\ominus$, for this reaction are given in the table below.

Use these values to calculate $\Delta H_{\text{reaction}}^\ominus$ for the synthesis of DME, using the following equation. Include a sign in your answer.

State Hess' Law.

Calculate the quantity of heat produced in experiment 1, stating your units.

Use relevant data from the Data Booklet and assume that all solutions have the same specific heat capacity as water.

Use your answer to (ii) to calculate the enthalpy change per mole of K₂CO₃.

Give your answer in kJ mol⁻¹ and include a sign in your answer.

Explain why the hydrochloric acid must be in an excess.

Calculate the quantity of heat absorbed in experiment 2.

Use your answer to (ii) to calculate the enthalpy change per mole of KHCO₃.

Give your answer in kJ mol⁻¹ and include a sign in your answer.

When KHCO₃ is heated, it decomposes into K₂CO₃, CO₂ and H₂O.

Use Hess' Law and your answers to (b)(iii) and (c)(iii) to calculate the enthalpy change for this reaction.

Give your answer in kJ mol⁻¹ and include a sign in your answer.

State Hess’ Law.

Calculate the quantity of heat produced in experiment 1, stating your units.

Use relevant data from the Data Booklet and assume that all solutions have the same specific heat capacity as water.

Use your answer to (ii) to calculate the enthalpy change per mole of $\text{K}_2\text{CO}_3$.

Give your answer in kJ mol⁻¹ and include a sign in your answer.

Explain why the hydrochloric acid must be in an excess.

Calculate the quantity of heat absorbed in experiment 2.

Use your answer to (ii) to calculate the enthalpy change per mole of $\text{KHCO}_3$.

Give your answer in kJ mol⁻¹ and include a sign in your answer.

When $\text{KHCO}_3$ is heated, it decomposes into $\text{K}_2\text{CO}_3$, $\text{CO}_2$ and $\text{H}_2\text{O}$.

Use Hess’ Law and your answers to (b)(iii) and (c)(iii) to calculate the enthalpy change for this reaction.

Give your answer in kJ mol⁻¹ and include a sign in your answer.

Explain the meaning of the term standard enthalpy change of reaction.

Calculate the amount of heat energy transferred to the water during this dissolving process.

You can assume that the specific heat capacity of the solution is the same as that of water, $4.18\text{ J g}^{-1}\text{ K}^{-1}$.

Calculate the enthalpy change of solution, $\Delta H_{\text{soln}}$, of $\text{MgSO}_4\text{(s)}$.

You must include a sign with your answer.

In the second experiment, the enthalpy change of solution for the hydrated salt, $\text{MgSO}_4\cdot 7\text{H}_2\text{O(s)}$, was calculated and found to be $+9.60\text{ kJ mol}^{-1}$.

Use the equation below for the hydration of anhydrous magnesium sulfate to construct a suitable, fully labelled energy cycle that will allow you to calculate the enthalpy change for this reaction, $\Delta H_{\text{hyd}} \text{ MgSO}_4$.

Calculate the enthalpy change for this reaction, $\Delta H_{\text{hyd}} \text{ MgSO}_4$. Include a sign in your answer.