In an experiment to measure the heat of reaction (\Delta H) for the reaction between hydrochloric acid (HCl) and sodium hydroxide (NaOH), 100 cm³ of 2M HCl were added to 100 cm² of 2M NaOH in the apparatus shown in the diagram - Leaving Cert Chemistry - Question 3 - 2012

An exothermic reaction is a type of chemical reaction that releases heat to the surroundings. This means the energy of the products is lower than that of the reactants, resulting in a rise in temperature of the surrounding environment. In this experiment, the reaction between hydrochloric acid and sodium hydroxide produces heat.

The evidence that indicates the reaction is exothermic is the observed increase in temperature of the solution during the reaction. As the reaction occurs, the thermometer will show a rise in temperature, confirming that heat is being released into the mixture.

1. Polystyrene cup: A polystyrene cup serves as a poor conductor of heat and helps to insulate the reaction mixture, thereby minimizing heat loss to the surroundings.

2. Cover: Using a cover helps to reduce the chances of heat escaping upwards, further insulating the reaction and conserving heat within the system.

To calculate the number of moles of HCl:

1. Use the formula: $\text{Moles} = \frac{\text{Volume (L)} \times \text{Concentration (mol/L)}}{1000}$

2. Convert 100 cm² to L: 100 cm² = 0.1 L.

3. Substitute the values: $\text{Moles} = \frac{0.1 \times 2}{1} = 0.2 \text{ moles}$

From the experiment, the heat produced from the reaction can be determined as follows:

1. The heat produced is 57 kJ when 0.2 moles of HCl completely react. Therefore, the heat produced per mole is: $\frac{57 kJ}{0.2 \, \text{moles}} = 285 \text{ kJ/mol}$.

2. For 1 mole of HCl:

   • The heat produced will be 285 kJ.

To find the heat of reaction (\Delta H):

1. Given that 11.4 K rise corresponds to the energy released:

   • The relationship is determined using the heat capacity.

2. The calculation will be: $\Delta H = \frac{11.4 K}{0.2} \times 57 kJ \approx 57 kJ \, \text{mol}^{-1}$.

The symbol indicates that hydrochloric acid is corrosive. This means that it can cause damage to living tissues as well as materials upon contact, highlighting the need for careful handling.