The enthalpy changes H1, H2, and H₃ cannot be identified without a reaction diagram or further context.

(d) (i)

• A strong acid completely dissociates in water to produce hydrogen ions.
• A weak acid only partially dissociates in water, establishing an equilibrium between the undissociated acid and its ions.

(d) (ii)

Sulphuric acid ($\text{H}_2\text{SO}_4$) is a strong acid and is assumed to fully dissociate both protons in dilute solutions for pH calculations.

Since 1 mole of $\text{H}_2\text{SO}_4$ produces 2 moles of $\text{H}^+$ ions:

(d) (iii)

• Maintaining a stable pH in biological systems, such as blood.
• Controlling the pH of solutions in chemical reactions or industrial processes.

(e) (i)

The reaction is: $2\text{NO(g)} + \text{O}_2\text{(g)} \rightleftharpoons 2\text{NO}_2\text{(g)}$

$[\text{NO}] = 0.05 \text{ moldm}^{-3}$
$[\text{O}_2] = 0.13 \text{ moldm}^{-3}$
$[\text{NO}_2] = 15.50 \text{ moldm}^{-3}$

(e) (ii)

Reactants: $2\text{NO(g)} + \text{O}_2\text{(g)} \implies 2 + 1 = 3$ moles of gas.
Products: $2\text{NO}_2\text{(g)} \implies 2$ moles of gas.

A decrease in pressure will shift the equilibrium to the side with a greater number of moles of gas to counteract the change. Since the reactant side has 3 moles of gas and the product side has 2 moles of gas, the equilibrium will shift towards the reactants.
The equilibrium position will shift to the left, favoring the formation of reactants ($\text{NO}$ and $\text{O}_2$).