Chemical Energetics

A student mixes $25.0\text{ cm}^3$ of $0.100\text{ mol dm}^{-3}$ sodium hydroxide solution with $25.0\text{ cm}^3$ of $0.100\text{ mol dm}^{-3}$ hydrochloric acid and the student records a temperature rise of $2.50^\circ\text{C}$.

What is the enthalpy change of the reaction per mole of NaOH?

Options

A   $-209\text{ kJ mol}^{-1}$
B   $-104.5\text{ kJ mol}^{-1}$
C   $-209\text{ J mol}^{-1}$
D   $-522.5\text{ J mol}^{-1}$

Carbon monoxide and methanol can react together to form ethanoic acid.

$$\text{CO}(\text{g}) + \text{CH}_3\text{OH}(\text{l}) \xrightarrow{\Delta H_{\text{r}}^\ominus} \text{CH}_3\text{CO}_2\text{H}(\text{l})$$

Standard enthalpy changes of combustion are given in the table.

What is the value for $\Delta H_{\text{r}}^\ominus$ for the reaction between carbon monoxide and methanol?

Options

A   $-1883.1\text{ kJ mol}^{-1}$
B   $-134.9\text{ kJ mol}^{-1}$
C   $+134.9\text{ kJ mol}^{-1}$
D   $+1883.1\text{ kJ mol}^{-1}$

All the reactants and products of an exothermic reaction are gaseous.

Which statement about this reaction is correct?

Options

A   The total bond energy of the products is less than the total bond energy of the reactants, and $\Delta H$ for the reaction is negative.
B   The total bond energy of the products is less than the total bond energy of the reactants, and $\Delta H$ for the reaction is positive.
C   The total bond energy of the products is more than the total bond energy of the reactants, and $\Delta H$ for the reaction is negative.
D   The total bond energy of the products is more than the total bond energy of the reactants, and $\Delta H$ for the reaction is positive.

The reaction of hydrogen with oxygen is shown.

$$2\text{H}_2(\text{g}) + \text{O}_2(\text{g}) \rightarrow 2\text{H}_2\text{O}(\text{l})$$

Which expression corresponds to the standard enthalpy change of this reaction?

Options

A   $2 \times \Delta H_{\text{f}}^{\ominus}(\text{H}_2\text{O})$
B   $\Delta H_{\text{c}}^{\ominus}(\text{H}_2\text{O}) - \Delta H_{\text{c}}^{\ominus}(\text{H}_2)$
C   $\Delta H_{\text{c}}^{\ominus}(\text{H}_2)$
D   $2 \times \Delta H_{\text{f}}^{\ominus}(\text{H}_2\text{O}) + 2 \times \Delta H_{\text{c}}^{\ominus}(\text{H}_2)$

$50 \text{ cm}^3$ of $1.0 \text{ mol dm}^{-3}$ $\text{H}_2\text{SO}_4$ is added to $100 \text{ cm}^3$ of $1.0 \text{ mol dm}^{-3}$ $\text{NaOH}$ in an insulated vessel.

Both solutions are at a temperature of $20\text{ }^{\circ}\text{C}$ before mixing. After mixing, the temperature rises and the highest temperature reached is $29\text{ }^{\circ}\text{C}$.

Assume that:

• all the energy released in the reaction goes into raising the temperature of the aqueous reaction mixture
• the specific heat capacity of the mixture is $4.2 \text{ J cm}^{-3} \text{ K}^{-1}$.

What is the value of the enthalpy of neutralisation determined from this experiment?

Options

A   $-113.4 \text{ kJ mol}^{-1}$
B   $-56.7 \text{ kJ mol}^{-1}$
C   $-37.8 \text{ kJ mol}^{-1}$
D   $-18.9 \text{ kJ mol}^{-1}$

Some standard enthalpy of combustion data are given.

Using these data, what is the enthalpy change of formation of methanol?

Options

A   $-240 \text{ kJ mol}^{-1}$
B   $-46 \text{ kJ mol}^{-1}$
C   $46 \text{ kJ mol}^{-1}$
D   $240 \text{ kJ mol}^{-1}$

The average intermolecular forces in water are much stronger than the average intermolecular forces in steam.

The average intermolecular forces in ice are slightly stronger than the average intermolecular forces in water.

Enthalpy changes are associated with the equilibrium processes shown.

$$\begin{aligned} \text{H}_2\text{O(l)} &\rightleftharpoons \text{H}_2\text{O(g)} \quad \Delta H_\text{b} \\ \text{H}_2\text{O(s)} &\rightleftharpoons \text{H}_2\text{O(l)} \quad \Delta H_\text{m} \end{aligned}$$

Which statements are correct?

1 $\Delta H_\text{b}$ and $\Delta H_\text{m}$ are both negative.
2 $\Delta H_\text{b}$ is greater than $\Delta H_\text{m}$.
3 The intermolecular forces in ice and water are of the same type.

Options

A   1, 2 and 3
B   1 and 2 only
C   1 and 3 only
D   2 and 3 only

Under certain conditions, $\text{CCl}_4$ and $\text{H}_2\text{O}$ react as shown. The activation energy for the reaction is $+62\text{ kJ mol}^{-1}$.

$$\text{CCl}_4 + 2\text{H}_2\text{O} \rightarrow \text{CO}_2 + 4\text{HCl} \quad \Delta H = -61.5\text{ kJ mol}^{-1}$$

Which enthalpy profile diagram best fits this reaction?

Options

The first stage in the industrial production of nitric acid from ammonia can be represented by the following equation.

$$4\text{NH}_3\text{(g)} + 5\text{O}_2\text{(g)} \rightleftharpoons 4\text{NO(g)} + 6\text{H}_2\text{O(g)}$$

Using the following standard enthalpy change of formation data, what is the value of the standard enthalpy change, $\Delta H^\ominus$, for this reaction?

Options

A   $+905.2\text{ kJ mol}^{-1}$
B   $-105.4\text{ kJ mol}^{-1}$
C   $-905.2\text{ kJ mol}^{-1}$
D   $-1274.0\text{ kJ mol}^{-1}$

The equation for the reaction of nitrogen with hydrogen is shown.

$$\text{N}_2\text{(g)} + 3\text{H}_2\text{(g)} \rightleftharpoons 2\text{NH}_3\text{(g)} \quad \Delta H_r^\ominus = -92.2\text{ kJ mol}^{-1}$$

Which statement is correct?

Options

A   $\Delta H_r^\ominus$ is measured at $298\text{ }^\circ\text{C}$.
B   $\Delta H_r^\ominus$ is measured at $101\text{ kPa}$.
C   $\Delta H_r^\ominus$ represents the standard enthalpy change for the formation of ammonia gas.
D   $\Delta H_r^\ominus$ represents the enthalpy change when $1.0\text{ mol}$ of $\text{N}_2\text{(g)}$ reacts with $1.0\text{ mol}$ of $\text{H}_2\text{(g)}$.