Describe an experiment to determine the enthalpy change of reaction between sodium carbonate and hydrochloric acid, including how to measure temperature changes over time.

Plot a graph of temperature versus time. Extrapolate the cooling curve (after the maximum temperature is reached) back to the time of mixing (when Solid A was added, $t=2\frac{1}{2}$ minutes) to find the theoretical maximum temperature. The initial temperature is recorded at $t=0$. The temperature change ($\Delta T$) is the difference between the extrapolated maximum temperature and the initial temperature.

The heat change ($Q$) is calculated using the formula:

where:

• $m$ is the mass of the solution. Assuming the density of the $\text{HCl}$ solution is approximately $1 \text{ g cm}^{-3}$, the mass of $25 \text{ cm}^3$ of solution is $25 \text{ g}$.
• $c$ is the specific heat capacity of the solution. Assume it is the same as water, $4.18 \text{ J g}^{-1} \text{ °C}^{-1}$.
• $\Delta T$ is the temperature change determined from the graph.

The reaction is:

The moles of $\text{HCl}$ used are:

Since the mass of Solid A ($\text{Na}_2\text{CO}_3$) is not given, you would need this information from the experiment to determine the moles of $\text{Na}_2\text{CO}_3$ and identify the limiting reactant. For this explanation, we assume $\text{HCl}$ is the limiting reactant or that the calculation is based on the moles of $\text{HCl}$ if $\text{Na}_2\text{CO}_3$ is in excess.

The enthalpy change ($\Delta H$) is the heat change per mole of the limiting reactant.

The negative sign indicates that if the temperature increases (exothermic reaction), $\Delta H$ is negative. The units will typically be $\text{J mol}^{-1}$ or $\text{kJ mol}^{-1}$.

Without the experimental data, a numerical answer for $\Delta T$, $Q$, or $\Delta H$ cannot be provided. The final answer would be the calculated value of $\Delta H$ in $\text{kJ mol}^{-1}$.