Explain why HI has a higher boiling point than HCl and HBr.
The bar chart gives the boiling points of HCl, HBr and HI. The boiling point of HF is not included. Hydrogen bonds are formed between HF molecules. Draw a bar on the bar chart to predict the boiling point of HF. Explain your answer.
The standard enthalpy change of formation, $\Delta H_f^{\circ}$, of $\text{HI}(g)$ is $+26.5\,\text{kJ mol}^{-1}$. Define the term standard enthalpy change of formation.
$\text{HI}(g)$ can be made by reacting $\text{H}_2(g)$ with $\text{I}_2(g)$. The reaction is reversible, and at high temperatures equilibrium is reached rapidly. $\text{H}_2(g) + \text{I}_2(g) \rightleftharpoons 2\text{HI}(g)$. Construct an expression for the equilibrium constant, $K_p$, for the reaction of $\text{H}_2(g)$ and $\text{I}_2(g)$ to form $\text{HI}(g)$.
The equilibrium partial pressures of the gases at $200^{\circ}\text{C}$ are as follows: $p_{\text{H}_2(g)} = 895\,\text{Pa}$, $p_{\text{I}_2(g)} = 895\,\text{Pa}$, $p_{\text{HI}(g)} = 4800\,\text{Pa}$. Calculate $K_p$ for this reaction.
State how the value of $K_p$ would change, if at all, if the reaction were carried out at $100^{\circ}\text{C}$ rather than $200^{\circ}\text{C}$. Explain your answer.
HI reacts with oxygen to form iodine and water. Construct an equation for the reaction of HI with oxygen.
Explain, with reference to oxidation numbers, why this reaction is a redox reaction.
$\text{HI}(g)$ can also be made by reacting $\text{I}_2(g)$ with hydrazine, $\text{N}_2\text{H}_4(g)$. $2\text{I}_2(g) + \text{N}_2\text{H}_4(g) \rightarrow 4\text{HI}(g) + \text{N}_2(g)$. State the change in pressure that would occur when $2\,\text{mol}$ $\text{I}_2(g)$ fully reacts with $1\,\text{mol}$ $\text{N}_2\text{H}_4(g)$ in a sealed container at constant temperature. Explain your answer.
In the laboratory, HI(aq) can be formed in a two-step process. step 1: $\text{3I}_2$(s) $+$ $\text{2P}$(s) $\rightarrow$ $\text{2PI}_3$(s) step 2: $\text{PI}_3$(s) $+$ $\text{3H}_2\text{O}$(l) $\rightarrow$ $\text{H}_3\text{PO}_3$(aq) $+$ $\text{3HI}$(aq) Draw a ‘dot-and-cross’ diagram of a $\text{PI}_3$ molecule.
Name the type of reaction in step 2.
$\text{H}_3\text{PO}_3$(aq) and $\text{HI}$(aq) are both strong Brønsted-Lowry acids. Give the meaning of the term strong Brønsted-Lowry acid.
Give the formula of the conjugate base of $\text{H}_3\text{PO}_3$.
HI(g) reacts with propene, $\text{CH}_3\text{CH}=\text{CH}_2$(g), to form a mixture of 1-iodopropane and 2-iodopropane. Identify which of 1-iodopropane and 2-iodopropane is the major product of this reaction. Explain your answer.
Complete the diagram to show the mechanism of the reaction between HI and $\text{CH}_3\text{CH}=\text{CH}_2$ that forms the major product identified in (g)(i). Include curly arrows, lone pairs of electrons and charges as necessary.