carbon based fuels - Unit 3 AOS 1

Question 1

Fuel

Answer 1

• fuels are substances used to produce energy
• they have chemical energy stored in them which can be converted into electrical energy
• it is usually reacted with oxygen to produce energy

Question 2

uses of fuels

Answer 2

• ## local level (petrol in car)

Question 3

renewable fuel

Answer 3

• one that can be replenished by natural processes within a relatively short period of time.
• they are sustainable and the chances of these fuels running out is very low.

Question 4

non-renewable fuel

Answer 4

• one that cannot be replenished at the rate it is used

Question 5

Fossil fuels

Answer 5

• fuels formed under the earth’s crust from the chemical decomposition of plant and animal matter
• contains chemical energy that can be converted into electrical, heat or chemical energy
• chemical decomposition takes a long period of time
• created by fossilisation where a dead organism is buried in relatively low oxygen conditions under intense pressures and heat

Question 6

coal

Answer 6

• a black or brown rock consisting of carbonised plant matter formed from the effects of pressure, heat and moisture.
• a mixture of large molecules made from hydrogen, nitrogen and sulphur formed by the partial decay of plant and animal matter
• vegetation - peat - brown coal - black coal
• from peat to black coal, water content decreases and carbon and energy content increases
• coal is bad for the environment as the combustion of it produces carbon dioxide

Question 7

petrol (crude oil)

Answer 7

• a mixture of hydrocarbons under the earths crust
• the hydrocarbons have different chain lengths
• is not useful itself as a fuel but contains many useful compounds
• separated by fractional distillation

Question 8

fractional distillation of crude oil

Answer 8

• crude oil has a mixture of different hydrocarbons, each with different chain lengths
• the longer the molecule, the stronger the intermolecular forces will be, requiring more energy to be broken
• long molecules - higher boiling points
• short molecules - lower boiling points

Question 9

fractional distillation of crude oil process

Answer 9

• crude oi is heated to a high temperature outside of the fractionating column
• when it is a t a certain temperature, it will be pumped into the bottom of the column
• at the bottom of the chamber where the temperature is high, some long chain molecules return to liquid and are collected at the bottom
• molecules rise up the column making their way through vents
• depending of molecules boiling points, they will eventually get too cool and condense to liquid where they can be collected in their tray.
• molecules with low boiling points will condense much high in the column

Question 10

natural gas (coal seam gas)

Answer 10

• found under the earths crust in coal deposits, in layers of rocks or in petroleum deposits
• composed of methane and other hydrocarbons
• it accessed by drilling and extracted by fracking

Question 11

renewability of fossil fuels

energy efficiency of fossil fuels

environmental impact of fossil fuels

Answer 11

• fossil fuels are considered non-renewable because they take a long time to form and so cannot be replenished quickly or at the rate they are used
• fossil fuels are more energy efficient.
• burning fossil fuels can produce pollutants such as SO2, contributing to acid rain
• accumulation of gases in the atmosphere can add to the greenhouse effect
• drilling disrupts natural landscapes

Question 12

bio fuels

Answer 12

• sourced from organic matter such as wheat, sugarcane and soy

Question 13

biogas

Answer 13

• a mixture of gases released by the anaerobic breakdown of organic matter
• mostly composed of methane and carbon dioxide
• bacteria breakdown complex molecules into smaller compounds
• variuos macromolecules broken down tp produce the gas (carbohydrates and proteins)

Question 14

biodiesel

Answer 14

• a mixture of organic compounds called esters that are produced from combining fats and alcohol in a transesterification reaction.
• triglyceride + methanol → fatty acid methyl esters + glycerol

Question 15

bioethanol

Answer 15

• a fuel produced by the fermentation of sugars and starches into organic matter called biomass
• conducted by yeast
• glucose solution → bioethanol solution + carbon dioxide
• fermentation conducted by yeast followed by distillation to remove water
• the ethanol needs to be separated from water
• it goes from 5-21% V/V to 100% V/V

Question 16

renewability of biofuels

energy efficiency of biofuels

environmental impact of biofuels

Answer 16

• biofuels are considered renewable because they can be replenished quickly
• biofuels are less efficient that due to the presence ox oxygen. They require more fuel to produce the same amount of energy.
• bioethanol is carbon neutral because the production of it released carbon dioxide however this is taken in by plants through photosynthesis. - This means there is no net production of carbon dioxide.
• biofuels are good foe waste management
• they are already partially oxidised so require less oxygen to fully combust.

Question 17

carbohydrates

Answer 17

• heat of combustion: 16kj g-1
• made form elements carbon, hydrogen and oxygen
• usually polymers of glucose
• during digestion, enzymes in out saliva ans small intestine break down starch into glucose
• this glucose is then transported to our cells where respiration can occur

Question 18

protein

Answer 18

• heat of combustion: 17kj g-1
• proteins are realy used for energy as they have so many other important roles within the body
• protein will be used as a last resort

Question 19

fats and oils

Answer 19

• heat of combustion: 37
• higher energy value due to degree that they can be oxidised and can release energy
• triglycerides - large non-polar molecules with three log hydrocarbon chains attached to a glycerol molecule
• digestion breaks down fats which can then be oxidised, releasing energy.

Question 20

cellular respiration

Answer 20

• organism convert glucose into energy
• glucose is oxidised into carbon dioxide
• C6H12O6 + 6O2 → 6H2O + 6CO2
• exothermic

Question 21

photosynthesis

Answer 21

• plants convert light energy into chemical energy in the form of glucose
• light is absorbed by chlorophyll which is then used to split water into hydrogen and oxygen ions
• the hydrogen ions are used to built carbohydrates
  6CO2 + H20 → C6H12O6 + 6O2
• endothermic

Question 22

exothermic reaction

Answer 22

• reactions that release energy
• will feel form
• energy of products is more than reactants
• negative ΔH

Question 23

endothermic reactions

Answer 23

• reactions that absorb heat
• will feel cool
• energy of reactants is more than products
• positive ΔH

Question 24

making and breaking bonds

Answer 24

• to break bonds, energy is taken in (endothermic)
• to make bonds, energy is released (exothermic)

Question 25

ΔH

Answer 25

• change in enthalpy of reactants and products
• ΔH = energy of products - energy of reactants

Question 26

activation energy

Answer 26

• the energy required break the bonds of the reactants to the reaction can proceed

Question 27

combustion reactions

Answer 27

• occur between oxygen and a fuel
• exothermic

Question 28

complete combustion

Answer 28

• occur when oxygen is in excess
• produces CO2 and H2O

Question 29

incomplete combustion

Answer 29

• occurs when oxygen is limited
• produces carbon products like CO or C

Question 30

thermochemical equations

Answer 30

• a balanced equation that includes the enthalpy change of a reaction

Question 31

determining limiting reactant

Answer 31

• divide mole by the coefficient and the smaller number is the limiting reactant

Question 32

heat of combustion

Answer 32

the energy released when a specific amount of a substance reacts completelty with oxygen