5, 6 for test 3

Question 1

Sustainable fuel source

Answer 1

Can meet current energy demand without being depleted and causes no harm to the environment

Question 2

Fossil fuel

Answer 2

Formed over millions of years from chemical changes to remains of organic materials.

Question 3

Bio fuel

Answer 3

Fuel produced from biomass (plant material)

Question 4

Renewable fuel

Answer 4

Can be replaced as fast as it is consumed. Eg Biofuel made from biomass

Question 5

Activation energy

Answer 5

Minimum amount of energy that must be overcome for a chemical reaction to occur. Energy from reactant potential energy to transition state.

Question 6

Transition state

Answer 6

Peak of the activation energy before the formation of products

Question 7

energy output of a fuel

Answer 7

amount of energy released when a fuel undergoes combustion. Fossil fuels generally have a higher energy output per unit of mass then biofuels

Question 8

Carbon emissions of a fuel

Answer 8

Release of CO2 (greenhouse gas) into the atmosphere when a fuel is combusted to produce energy.

Question 9

In terms of bond breaking and forming explain the shape of the energy profile (exo)

Answer 9

• exothermic process
• less energy is absorbed to break existing bonds than is released when new bonds form
• enthalpy products is less than reactants (surplus of energy is released into the surroundings as heat)

Question 10

explain the shape of the energy profile in terms of Law of Conservation of Energy

Answer 10

• Products have lower enthalpy than reactants
• Law states that energy can’t be created or destroyed so surplus of energy is transferred from the system to the surroundings
• energy changes form and so is always conserved

Question 11

Explain why Octane is not considered a sustainable fuel source

Answer 11

• Sustainable fuel source can meet current demand without being depletes and causes no harm to the environment.
• Octane is a ff so cant meet current energy demand without being completely consumed.
• Produces net output of CO2 (green house gas) that contributed to climate change.
  Therefore not considered to be sustainable

Question 12

Biofuels are sustainable

Answer 12

Made from biomass - crops can be replaced as fast as they are consumed
Does not harm the environment - CO2 released is reabsorbed in photosynthesis when more biomass is grown for bio fuel (carbon neutral cycle)

Question 13

Explain why is an exothermic reaction

Answer 13

Has energy profile of exothermic reaction:
- Energy needed to break bonds is less than energy released to form bonds.
- Products have lower enthalpy than reactants as surplus of energy is released into surroundings
- As such it releases heat energy so is exothermic

Question 14

Enthalpy - delta h

Answer 14

stored chemical energy. Enthalpy of any chemical reaction changes as our reactants turn into products. Delta H is change in enthalpy from potential energy of reactants to products.

Question 15

Exothermic reaction
- enthalpy change
- example

Answer 15

Releases heat in the form of energy, feels hot. Enthalpy decreases during reaction. Combustion is exothermic, releasing stores chemical potential energy

Question 16

Endothermic reaction
- enthalpy change
- example

Answer 16

Absorbs heat and therefore feels cold. Positive enthalpy change. Cold pack.

Question 17

Start a chemical reaction

Answer 17

In order to break existing bonds and reach the transition state energy needs to be added to the system. Referred as endothermic part of any thermochemical reaction

Question 18

Reactant chemical potential energy to transition state

Answer 18

Endothermic

Question 19

Transition state to product

Answer 19

Bond formation releases energy so is an exothermic process

Question 20

Overall enthalpy change

Answer 20

determines whether a reaction is endothermic (pos delta H) or exothermic (neg delta H)

Question 21

Why is bond breaking endothermic

Answer 21

In bond breaking the attractive forces that hold atoms together in molecules must be broken, this requires energy to overcome the electrostatic attraction. As such bond breaking absorbs energy from the surroundings.

Question 22

Why bond formation is exothermic

Answer 22

When new bonds form in the products, energy is released. Results in decrease in potential energy as atoms are in a more stable configuration. Release energy in the form of heat.

Question 23

Solid to liquid state

Answer 23

Endothermic as absorbs heat to change state. Potential energy increases which is why you need to add energy to the system in the form of heat.

Question 24

Gas to liquid

Answer 24

Exothermic as loose kinetic energy, resulting in decrease in temperature and the release of heat energy.

Question 25

Chemical reaction
Physical change

Answer 25

New substance formed
Change in state

Question 26

1.00 tonne

Answer 26

10^6

Question 27

Eheat released on combustion

Answer 27

Number of moles of fuel x energy (kJ) released per mole of fuel

Question 28

Energy transferred vs transformed

Answer 28

Energy transferred - absorbed/released into surroundings
Energy transformed - heat energy is transformed into stored chemical potential energy to break bonds of reactants

Question 29

Thermochemical equations

Answer 29

Involves heat energy as a product/reactant

Question 30

Bio fuel instead of fossil fuels

Answer 30

A - renewable less carbon emissions
D - less energy output