Define, using an equation that includes state symbols, the standard enthalpy change of formation of carbon dioxide.
The reaction that makes methanol has relevant $\Delta H_f^\circ$ values listed below. Use them to work out $\Delta H_{\text{reaction}}^\circ$ for this methanol synthesis. Include the sign in your answer. $\text{CO}_2(g) + 3\text{H}_2(g) \rightleftharpoons \text{CH}_3\text{OH}(g) + \text{H}_2\text{O}(g)$
Suggest one environmental advantage that could result from this reaction. Explain your answer.
Methanol is synthesised at around $500\,\text{K}$ under a pressure between $40$ and $100$ atmospheres (between $4 \times 10^6\,\text{Pa}$ and $10 \times 10^7\,\text{Pa}$) and in the presence of a catalyst. These conditions influence both the reaction rate and the equilibrium yield. Explain the effect of higher temperature, higher pressure, and the use of a catalyst on the equilibrium yield of methanol.