VCE Unit 3 Chemistry AOS1 Fuel choices and obtaining energy from fuels

Renewable fuel

A fuel that can be naturally restored or replenished faster than it is consumed.

Non-renewable fuel

A fuel that is not being formed as fast as we are using it e.g. coal, oil, and gas. Current reserves of these fuels will eventually run out.

Equation for volume of a gas at SLC

V = n*Vm

Three fossil fuels

coal, crude oil, natural gas

Three biofuels

biogas, bioethanol, biodiesel

Composition of crude oil

A mixture of hydrocarbons (mostly alkanes)

Biofuels

Fuels derived from plant materials e.g. grain, sugarcane or vegetable waste

Carbon neutral

Making no net release of carbon dioxide to the atmosphere

Burning biochemical fuels is not considered to increase atmospheric CO2 levels as....

the photosynthesis process used to produce the plant matter removes CO2 from the atmosphere, making them carbon neutral.

How is bioethanol formed?

Starch in plants is broken down into glucose by enzymes and is then fermented to ethanol and carbon dioxide in the absence of oxygen.

Composition of biodiesel

A mixture of esters

How is biodiesel formed?

Through the reaction of vegetable oils and an alcohol. The oil is first hydrolysed into glycerol and 3 fatty acid chains. The fatty acids then react with alcohol to form esters.

Three advantages of biodiesel

1. biodegradable

2. non-toxic

3.produces fewer pollutants in vehicle emissions

SI unit of energy

Joule (J)

Balanced thermochemical equation for the combustion of methanol (including states)

CH3OH(l)+ 1.5 O2(g)⟶CO2(g)+2H2O(l) ∆H = −726 kJ mol-1

Balanced thermochemical equation for the combustion of ethanol (including states)

C2H5OH(l) + 3O2(g) ⟶ 2CO2(g) + 3H2O(l) ∆H = −1360 kJ mol-1

Balanced thermochemical equation for the combustion of octane (including states)

C8H18(l) + 7.5O2(g) ⟶ 8CO2(g) + 9H2O(l) ∆H = −5460 kJ mol-1

Balanced thermochemical equation for the combustion of ethane (including states)

C2H6(g) + 4.5O2(g) ⟶ 2CO2(g) + 3H2O(l) ∆H = −1560 kJ mol-1

The ideal gas equation and units

PV = nRT

P in kPa, V in L, n in mol, T in K

SLC

Standard laboratory conditions (25 oC and 100 kPa)

relationship between heat energy and specific heat capacity

q = mc∆T

relationship between enthalpy and heat energy

∆H = q * x/n

To convert kJ mol-1 to kJ g-1 ____________________

divide by molar mass

To convert kJ g-1 to kJ mol-1 ____________________

multiply by molar mass

1 MJ tonne-1 = _________ kJ kg-1

1

1 kJ g-1 = _________ kJ kg-1

1000

Change in ∆H if a reaction is reversed.

Change sign.

Change in ∆H if reaction coefficients are multiplied by factor x.

Multiply ∆H by x.

Steps to calculate the enthalpy of combustion for a fuel used to heat a some water.

1. Calculate the heat energy absorbed by the water using the increase in temperature and q = mc∆T, where m is the mass of water and c is the specific heat capacity of water.

2. Assume that the heat energy absorbed by the water = the heat energy released by the fuel (unless told that the process was not 100 % efficient)

3. Calculate the enthalpy of combustion ∆H = q/n, where n is the mole of fuel burnt.