5, 6 for test 3 Flashcards
Sustainable fuel source
Can meet current energy demand without being depleted and causes no harm to the environment
Fossil fuel
Formed over millions of years from chemical changes to remains of organic materials.
Bio fuel
Fuel produced from biomass (plant material)
Renewable fuel
Can be replaced as fast as it is consumed. Eg Biofuel made from biomass
Activation energy
Minimum amount of energy that must be overcome for a chemical reaction to occur. Energy from reactant potential energy to transition state.
Transition state
Peak of the activation energy before the formation of products
energy output of a fuel
amount of energy released when a fuel undergoes combustion. Fossil fuels generally have a higher energy output per unit of mass then biofuels
Carbon emissions of a fuel
Release of CO2 (greenhouse gas) into the atmosphere when a fuel is combusted to produce energy.
In terms of bond breaking and forming explain the shape of the energy profile (exo)
- 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)
explain the shape of the energy profile in terms of Law of Conservation of Energy
- 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
Explain why Octane is not considered a sustainable fuel source
- 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
Biofuels are sustainable
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)
Explain why is an exothermic reaction
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
Enthalpy - delta h
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.
Exothermic reaction
- enthalpy change
- example
Releases heat in the form of energy, feels hot. Enthalpy decreases during reaction. Combustion is exothermic, releasing stores chemical potential energy
Endothermic reaction
- enthalpy change
- example
Absorbs heat and therefore feels cold. Positive enthalpy change. Cold pack.
Start a chemical reaction
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
Reactant chemical potential energy to transition state
Endothermic
Transition state to product
Bond formation releases energy so is an exothermic process
Overall enthalpy change
determines whether a reaction is endothermic (pos delta H) or exothermic (neg delta H)
Why is bond breaking endothermic
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.
Why bond formation is exothermic
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.
Solid to liquid state
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.
Gas to liquid
Exothermic as loose kinetic energy, resulting in decrease in temperature and the release of heat energy.
Chemical reaction
Physical change
New substance formed
Change in state
1.00 tonne
10^6
Eheat released on combustion
Number of moles of fuel x energy (kJ) released per mole of fuel
Energy transferred vs transformed
Energy transferred - absorbed/released into surroundings
Energy transformed - heat energy is transformed into stored chemical potential energy to break bonds of reactants
Thermochemical equations
Involves heat energy as a product/reactant
Bio fuel instead of fossil fuels
A - renewable less carbon emissions
D - less energy output
