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 cm³ 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 where heat is released into the surroundings as products form. This is shown by a decrease in temperature of the reaction mixture, and the net energy change (\Delta H) is negative.

1. Polystyrene Cup: The polystyrene cup is a poor conductor of heat, which helps to reduce heat loss.
2. Cover: The cover on the cup provides insulation by preventing heat from escaping upward, thus retaining more heat within the system.

The calculation for the number of moles is as follows:

Number of moles = concentration (mol/dm³) × volume (dm³)

Converting 100 cm³ to dm³ gives:

100 cm³ = 0.1 dm³

Therefore,:

Number of moles of HCl = 2 mol/dm³ × 0.1 dm³ = 0.2 moles.

To find the heat produced for 1 mole of HCl:

1. Heat produced from 0.2 moles of reaction: 1.14 kJ
2. Heat per mole = \frac{1.14 ext{ kJ}}{0.2 ext{ moles}} = 5.7 ext{ kJ/mol}

Therefore, for 1 mole of HCl, it produces 5.7 kJ of heat.

The heat of reaction (\Delta H) for this reaction is therefore -57 kJ mol⁻¹, indicating that the process is exothermic.

The symbol signifies that hydrochloric acid is a corrosive substance, indicating that it can cause severe chemical burns or destruction of tissues upon contact.