Reactivity: How Much, How Fast, and How Far? — Free Chemistry SL Practice Questions

Methanol is produced industrially from synthesis gas according to the reversible reaction: $$\text{CO}(g) + 2\text{H}_2(g) \rightleftharpoons \text{CH}_3\text{OH}(g)$$ A chemist mixes $1.00\,\text{mol}$ of $\text{CO}(g)$ and $2.00\,\text{mol}$ of $\text{H}_2(g)$ in a $10.0\,\text{dm}^3$ reactor at $500\,\text{K}$. At equilibrium, the concentration of $\text{CH}_3\text{OH}(g)$ is $0.0400\,\text{mol}\,\text{dm}^{-3}$.

The graph below shows how concentrations change over time for the reaction: $$\text{A}(g) \rightleftharpoons 2\text{B}(g) \quad \Delta H = +48\,\text{kJ mol}^{-1}$$ *(Concentration–time graph: $[\text{A}]$ starts at $1.0\,\text{mol dm}^{-3}$ and decreases; $[\text{B}]$ starts at $0$ and increases; both level off at $t = 5\,\text{min}$ with $[\text{A}]_{\text{eq}} = 0.40\,\text{mol dm}^{-3}$ and $[\text{B}]_{\text{eq}} = 1.20\,\text{mol dm}^{-3}$)*

Nitrosyl chloride, NOCl, decomposes at elevated temperatures according to the equation: $$2\text{NOCl}(g) \rightleftharpoons 2\text{NO}(g) + \text{Cl}_2(g)$$ A $2.00\,\text{dm}^3$ flask is filled with $0.600\,\text{mol}$ of $\text{NOCl}(g)$ and heated to $450\,\text{K}$. At equilibrium, the flask contains $0.200\,\text{mol}$ of $\text{Cl}_2(g)$.

Phosgene ($\text{COCl}_2$) is a toxic gas used in the industrial production of polyurethanes. It is formed by the reversible reaction: $$\text{CO}(g) + \text{Cl}_2(g) \rightleftharpoons \text{COCl}_2(g) \quad \Delta H < 0$$ In an experiment, $0.500\,\text{mol}$ of $\text{CO}(g)$ and $0.500\,\text{mol}$ of $\text{Cl}_2(g)$ are placed in a $5.00\,\text{dm}^3$ container at $600\,\text{K}$. At equilibrium, the concentration of $\text{COCl}_2(g)$ is $0.0600\,\text{mol}\,\text{dm}^{-3}$.

The Haber process for the production of ammonia is represented by the following equilibrium: $$N_2(g) + 3H_2(g) \rightleftharpoons 2NH_3(g) \qquad \Delta H = -92\,\text{kJ mol}^{-1}$$ In an industrial reactor, nitrogen and hydrogen in a $1:3$ mole ratio are passed over an iron catalyst at $450\,°\text{C}$ and $200\,\text{atm}$. The concentration of ammonia in the exit gas stream increases from zero until it reaches a constant value of $0.060\,\text{mol dm}^{-3}$ after $30$ minutes.

A student investigates the reaction between sodium carbonate ($\text{Na}_2\text{CO}_3$) and hydrochloric acid (HCl): $$\text{Na}_2\text{CO}_3(\text{s}) + 2\,\text{HCl}(\text{aq}) \rightarrow 2\,\text{NaCl}(\text{aq}) + \text{CO}_2(\text{g}) + \text{H}_2\text{O}(\text{l})$$ The student adds $2.65\,\text{g}$ of anhydrous sodium carbonate to a flask containing $50.0\,\text{cm}^3$ of $1.00\,\text{mol\,dm}^{-3}$ hydrochloric acid. After the reaction, the remaining acid is titrated with $0.200\,\text{mol\,dm}^{-3}$ sodium hydroxide solution, using phenolphthalein indicator. The titration requires $15.0\,\text{cm}^3$ of sodium hydroxide solution to reach the endpoint. - Molar mass of $\text{Na}_2\text{CO}_3 = 106.0\,\text{g\,mol}^{-1}$

Hydrazine ($\text{N}_2\text{H}_4$) is used as a rocket fuel, reacting with dinitrogen tetroxide ($\text{N}_2\text{O}_4$) in an exothermic reaction: $$2\text{N}_2\text{H}_4(l) + \text{N}_2\text{O}_4(l) \rightarrow 3\text{N}_2(g) + 4\text{H}_2\text{O}(g)$$ A spacecraft carries $320\,\text{kg}$ of $\text{N}_2\text{H}_4$ and $460\,\text{kg}$ of $\text{N}_2\text{O}_4$ for a mid-course correction manoeuvre. Molar masses: $\text{N}_2\text{H}_4 = 32.0\,\text{g\,mol}^{-1}$; $\text{N}_2\text{O}_4 = 92.0\,\text{g\,mol}^{-1}$; $\text{N}_2 = 28.0\,\text{g\,mol}^{-1}$

Iron(III) oxide ($\text{Fe}_2\text{O}_3$) reacts with carbon monoxide (CO) in a blast furnace: $$\text{Fe}_2\text{O}_3(s) + 3\text{CO}(g) \rightarrow 2\text{Fe}(s) + 3\text{CO}_2(g)$$ A sample of iron ore contains $80.0\%$ by mass $\text{Fe}_2\text{O}_3$ and $20.0\%$ inert impurities. Molar masses: $\text{Fe} = 55.8\,\text{g mol}^{-1}$, $\text{Fe}_2\text{O}_3 = 160\,\text{g mol}^{-1}$, $\text{Fe}_3\text{O}_4 = 232\,\text{g mol}^{-1}$

Zinc granules react with sulfuric acid: $$\text{Zn(s)} + \text{H}_2\text{SO}_4\text{(aq)} \rightarrow \text{ZnSO}_4\text{(aq)} + \text{H}_2\text{(g)}$$ A student places $5.0\,\text{g}$ of zinc granules into $100.0\,\text{cm}^3$ of $0.50\,\text{mol dm}^{-3}$ $\text{H}_2\text{SO}_4\text{(aq)}$ at $25\,°\text{C}$ and measures the volume of hydrogen gas collected every $30\,\text{s}$. The reaction is slow at first, then becomes faster, and finally slows down until it stops.

Magnesium ribbon reacts with dilute hydrochloric acid: $$\text{Mg}(s) + 2\text{HCl}(aq) \rightarrow \text{MgCl}_2(aq) + \text{H}_2(g)$$ A student performs two experiments using identical $3.0\,\text{cm}$ strips of magnesium ribbon and $50\,\text{cm}^3$ of $1.0\,\text{mol}\,\text{dm}^{-3}$ HCl. In Experiment X, the acid is at $20\,°\text{C}$. In Experiment Y, the acid is heated to $40\,°\text{C}$ before adding the magnesium. The volume of $\text{H}_2$ produced is measured at regular intervals. The student records the following initial rates of gas production: - Experiment X: $0.80\,\text{cm}^3\,\text{s}^{-1}$ - Experiment Y: $3.20\,\text{cm}^3\,\text{s}^{-1}$

The reaction between iodine and propanone in acidic solution is catalysed by hydrogen ions. $$\text{CH}_3\text{COCH}_3\text{(aq)} + \text{I}_2\text{(aq)} \rightarrow \text{CH}_3\text{COCH}_2\text{I(aq)} + \text{H}^+\text{(aq)} + \text{I}^-\text{(aq)}$$ A series of experiments was carried out at $25\,^\circ\text{C}$ to determine the rate law. Initial rates were measured by monitoring the disappearance of $\text{I}_2$ using colorimetry. The initial concentration of $\text{I}_2$ in all experiments was $5.0 \times 10^{-4}\,\text{mol dm}^{-3}$. Experiment — $[\text{CH}_3\text{COCH}_3] / \text{mol dm}^{-3}$ — $[\text{H}^+] / \text{mol dm}^{-3}$ — Initial rate $/ \text{mol dm}^{-3}\text{s}^{-1}$ 1 — $0.50$ — $0.10$ — $2.0 \times 10^{-6}$ 2 — $1.00$ — $0.10$ — $4.0 \times 10^{-6}$ 3 — $0.50$ — $0.20$ — $4.0 \times 10^{-6}$ 4 — $1.00$ — $0.20$ — $8.0 \times 10^{-6}$

Nitrogen dioxide, $\text{NO}_2$, decomposes at elevated temperatures: $$2\text{NO}_2(\text{g}) \rightarrow 2\text{NO}(\text{g}) + \text{O}_2(\text{g})$$ The reaction is second order with respect to $\text{NO}_2$. A student investigates the kinetics of this decomposition at $300\,^\circ\text{C}$ using a $1.00\,\text{dm}^3$ flask initially containing $0.200\,\text{mol}$ of $\text{NO}_2$. $$R = 8.31\,\text{J}\,\text{mol}^{-1}\,\text{K}^{-1}$$ $$k = 1.20 \times 10^{-2}\,\text{dm}^3\,\text{mol}^{-1}\,\text{s}^{-1} \text{ at } 300\,^\circ\text{C}$$

The Haber process for ammonia synthesis, $\text{N}_2\text{(g)} + 3\text{H}_2\text{(g)} \rightleftharpoons 2\text{NH}_3\text{(g)}$, has a high activation energy due to the strong triple bond in nitrogen. Industrial conditions use an iron catalyst approximately $450\,^\circ\text{C}$.