fuels and energy

Question 1

fuel

Answer 1

substance used to release energy

Question 2

types of fuels

Answer 2

• fossil fuels
  crude oil, coal, natural gas
• biofuels
  ethanol
• hydrogen
• nuclear

Question 3

crude oil

Answer 3

• contains large mixtures of hydrocarbons
• hydrocarbons only contain hydrogen and carbon
• non-renewable, gets used up faster than it forms
• petroleum is refined using fractional distillation

Question 4

refining petroleum

Answer 4

• a mixture of many different hydrocarbon-molecules containing the elements carbon and hydrogen
• to be useful, petroleum needs to be Separated into seperate hydrocarbon compounds.
• this is petroleum refining
  petroleum refining is done by fractional distillation, this separates hydrocarbons based on the lengths of their chains
  this process is carried out in a tower where temperature is strictly controlled. the tower is hotter at the bottom and cooler of the top
• Crude oil is pumped in and the mixture begins to boil and the molecules start to evaporate.
• Short chain molecules have lower boiling points and exit.
  at the top as gases:
  longer chain molecules have higher boiling points and enit at the bottom or remain as liquids or solids

Question 5

combustion

Answer 5

the burning of a fuel.

the refining of Petroleum/Crude Oil produces hydrocarbon s which can be used as fuel. Fuels are combusted or burnt to produce energy.

Question 6

combustion and pollution

Answer 6

during combustion fuels react with oxygen

Question 7

complete combustion

Answer 7

with excess oxygen
products- co2 and h2o

Question 8

incomplete combustion

Answer 8

limited oxygen
products- co and/or soot and water

Question 9

endothermic

Answer 9

• energy is absorbed from the surroundings
• can be observed by a decrease in surrounding temperature
  due to energy level of products being higher than reactant
• more energy is needed to break bonds in reactant than released making bonds in the product

Question 10

exothermic

Answer 10

energy is released into the
surrounding

can be observed by a temperature increase
of surroundings
due to energy level being higher than the product

more energy is released in bond making in the product rather than needed to break bonds in the reactant

Question 11

enthalpy change of a reaction

Answer 11

In any reaction bonds are being broken and new bonds are being formed.

Bond breaking absorbs energy (endothermic) and bond making releases energy (exothermic)

∆H is the difference between the energy required to break the bonds and the energy released when bonds are formed.

If more energy is absorbed than released, then the reaction is endothermic - ∆H is positive

If more energy is released than absorbed, then the reaction is exothermic - ∆H is negative

Question 12

bond energy

Answer 12

The amount of energy in kilojoules (kJ) associated with breaking or making 1 mole of chemical bonds in a molecule.

Question 13

bond breaking

Answer 13

All reactions must begin with reactant bonds being broken. This requires energy.

Question 14

bond making

Answer 14

New bonds must then be formed in products. This releases energy.

Question 15

enthalpy change

Answer 15

Is the change in the total energy associated with the substances which are reacting. Symbol = ΔH.

Question 16

ΔH

Answer 16

total bond energy bonds broken – total bond energy bonds made

Question 17

hydrogen-oxygen fuel cells

Answer 17

• Fuel cells directly convert the chemical energy in hydrogen to electricity, with pure water and heat as the only by products
• They are pollution free and can also have 2-3 times the efficiency of combustion energy sources.
• Petrol engines are less than 20% efficient in converting chemical energy into kinetic energy to move the car. Hydrogen fuel cell cars use up to 40-60% of the fuels energy.
• Fuel cells operate quietly and have fewer moving parts.

Question 18

reactions

Answer 18

anode- 2H2 — 4H+ + 4e-
cathode- O2 + 4H+ + 4e- —- 2H2O
net reaction- 2H2 + O2 — 2H2O

Question 19

advantages

Answer 19

• need only oxygen and hydrogen (produced from the electrolysis of water)
• Don’t produce any waste
• Last longer than batteries
• Less pollution to dispose of

Question 20

disadvantages

Answer 20

• Hydrogen is a gas so more space is needed to store than fossil fuels
• Explosive when mixed with air
• Storage is dangerous and difficult