International Baccalaureate IB Chemistry

Reactive metals, non-metals and organic compounds undergo combustion reactions when heated in oxygen.

Deduce equations for reactions of combustion, including hydrocarbons and alcohols.

Incomplete combustion of organic compounds, especially hydrocarbons, leads to the production of carbon monoxide and carbon.

Deduce equations for the incomplete combustion of hydrocarbons and alcohols.

For a generic alkane $\mathrm{C_{n}H_{2n+2}}$ the incomplete combustion can be written as  

$$\mathrm{C_{n}H_{2n+2} + \frac{n}{2}\,O_{2} \rightarrow n\,CO + (n+1)\,H_{2}O}$$  

or, when carbon is formed,  

$$\mathrm{C_{n}H_{2n+2} + \frac{n}{2}\,O_{2} \rightarrow n\,C + (n+1)\,H_{2}O}$$  

For a generic alcohol $\mathrm{C_{n}H_{2n+1}OH}$ (i.e., $\mathrm{C_{n}H_{2n+2}O}$) the incomplete combustion can be expressed as  

$$\mathrm{C_{n}H_{2n+2}O + \frac{n}{2}\,O_{2} \rightarrow n\,CO + (n+1)\,H_{2}O}$$  

or  

$$\mathrm{C_{n}H_{2n+2}O + \frac{n}{2}\,O_{2} \rightarrow n\,C + (n+1)\,H_{2}O}$$

Fossil fuels include coal, crude oil and natural gas, which have different advantages and disadvantages.

Evaluate the amount of carbon dioxide added to the atmosphere when different fuels burn. 

Understand the link between carbon dioxide levels and the greenhouse effect.

Biofuels are produced from the biological fixation of carbon over a short period of time through photosynthesis.

Understand the difference between renewable and non‑renewable energy sources. 

Consider the advantages and disadvantages of biofuels. The reactants and products of photosynthesis should be known.

A fuel cell can be used to convert chemical energy from a fuel directly to electrical energy.

Deduce half‑equations for the electrode reactions in a fuel cell. Hydrogen and methanol should be covered as fuels.

$$\mathrm{H_2 \rightarrow 2H^+ + 2e^-}$$
$$\mathrm{\frac{1}{2}O_2 + 2H^+ + 2e^- \rightarrow H_2O}$$

$$\mathrm{CH_3OH + H_2O \rightarrow CO_2 + 6H^+ + 6e^-}$$
$$\mathrm{\frac{3}{2}O_2 + 6H^+ + 6e^- \rightarrow 3H_2O}$$