Chem SAC1

Fuel

A substance that can easily release stored energy

Fossil fuel

non-renewable fuels such as coal, petrol and natural gas formed in the geological past from remains of living organisms

Bio-fuel

renewable fuels derived from plants or animals biogas, biodiesel and bioethanol

non renewable

resources that are used faster than they can be replaced

renewable

replenished in short period of time

Fossil fuel advantages

relatively high energy content, natural gas and petrol easy to transport

Fossil fuel disadvantages

Non renewable, high level emissions

Biofuel disadvantages

Lower energy content, limited supply of raw materials from which to produce it, bioethanol require use of farmland otherwise used for food production

biofuel advantages

renewable, can be made from waste material, CO2 absorbed during photosynthesis

Bio gas

Biogas is the gas released in the breakdown of organic waste by anaerobic (absence of oxygen) bacteria. Biogas mainly consists of methane and carbon dioxide it generates electricity via combustion however energy released per gram is lower than natural gas because methane content in biogas is much lower.

Biodiesel

Biodiesel is an ester produced from the reaction of a triglyceride and an alcohol. Triglyceride can be vegetable or animal oil alcohol is typically methanol

Bioethanol

Produced via fermentation which is carbohydrates converted into an alcohol with enzymes to catalyse reaction. Ethanol must be separated from water to make it useful as a fuel, distillation utilises different boiling points of the liquids to separate them

Fermentation reaction

C6H12O6 (aq) → 2CH3CH2OH (aq) + 2CO2 (g)

Exothermic reaction

Energy released in the form of heat into the atmosphere

enthalpy is negative

products have lower enthalpy than the reactants

forming bonds

The energy required to break bonds in the reactants is less than the energy released when new bonds are formed in the products.

Endothermic reaction

Heat energy absorbed from atmosphere

enthalpy is positive

products have greater enthalpy than reactants

breaking bonds

The energy required to break bonds in reactants is greater than the energy released when the new bonds are formed in the products.

Molar enthalpy change

the change in enthalpy per mol of a substance undergoing reaction kj mol-1

products minus reactants

Exothermic

Endothermic

Specific heat capacity

energy required in joules to increase 1 gram of a substance by 1 degree celcius without changing its state

Oxidising agent

is reduced and causes oxidation

Reducing agent

is oxidised causes reduction

Oxidation number increases

substance is oxidised therefore reducing agent

Oxidation number decreases

substance is reduced and therefor is the oxidising agent

cathode

reduction, electrons are reactants higher half equation in electrochemical series

anode

oxidation, electrons are products lower half equation in electrochemical series flipped

Accuracy

how close the experimental value is to the true value

precision

how close experimental values are to each other

random error

follow no regular pattern affect the precision

e.g error estimating second decimal place

temp variation solution not mixed consistently

variation in gas flow rate