Developing Fuels

A study of fuels and the contribution that chemists make to the development of better fuels.

Main topics:

 Desirable properties of a fuel;

 Hydrocarbons and alcohols as fuels;

 Available energy in fuels;

 Overcoming the problem of auto-ignition: alternatives to lead compounds;

 Exhaust emissions and control of exhaust pollutants;

 Alternative fuels.

Student check list. Can you?

(a) use the concept of amount of substance to perform calculations involving: volumes of gases, balanced chemical equations, enthalpy changes;

(b) explain and use the terms: exothermic, endothermic, standard state, enthalpy change of combustion, enthalpy change of reaction, enthalpy change of formation;

(c) interpret the pattern of enthalpy changes of combustion for successive members of an homologous series;

(d) calculate enthalpy changes from experimental results;

(e) use Hess’s Law and enthalpy cycles to calculate enthalpy changes;

(f) recall that bond-breaking is an endothermic process and bond-making is exothermic;

(g) explain and use the term: bond enthalpy;

(h) relate bond enthalpy to the length and strength of a bond;

(i) recognise members of these homologous series: alkanes, cycloalkanes, alkenes, arenes, alcohols, ethers;

(j) explain and use the terms: aliphatic, aromatic;

(k) use systematic nomenclature to name alkanes and alcohols;

(l) explain and use the term isomerism;

(m) recognise structural isomers;

(n) draw and interpret structural formulae (full, shortened and skeletal);

(o) relate molecular shape to structural formulae and be familiar with the use of models to represent molecular shape;

(p) describe and write balanced equations for the combustion (oxidation) of alkanes and alcohols;

(q) describe the effect of chain length and chain branching on the tendency of petrol towards auto-ignition which causes ‘knocking’ in a car engine;

(r) explain what is meant by the octane rating of a petrol and describe how it may be increased;

(s) describe the origin of pollutants from car exhausts: unburnt hydrocarbons, CO, CO₂, NOx,

SOx, and show awareness of the environmental implications;

(t) explain the formation of nitrogen monoxide (NO) in an internal combustion engine;

(u) explain and use the terms catalysis, catalyst, catalyst poison;

(v) outline a simple model to explain the function of a heterogeneous catalyst;

(w) describe the use of isomerisation, reforming and cracking reactions to improve the performance of hydrocarbon fuels;

(x) show awareness of the use of catalysts in isomerisation, reforming and cracking processes and in the control of exhaust emissions;

(y) discuss entropy in a qualitative manner, interpreting it as a measure of the number of ways that molecules can be arranged;

(z) show awareness of the differences in magnitude of the entropy of a solid, a liquid, a solution and a gas;

(aa) discuss the desirable properties of a fuel;

(bb) show awareness of the work of chemists in improving fuels and in searching for and developing fuels for the future: use of oxygenates, the hydrogen economy.