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Chapter 6 - Chemical Energetics - from my full syllabus notes from IGCSE Chemistry
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Chapter 6 from my full syllabus notes from IGCSE Chemistry
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Bonds:- Bond breaking is an endothermic process
- Bond forming is an exothermic process
Calculating the energy of a reaction using bond energies:
- Bond energy: the amount of energy needed to break a mole of a particular bond
- You will be given any bond energies you need in the exam
- If the energy change is positive then it shows energy is taken in from the surroundings
(endothermic)
- If the energy change is negative then it shows energy is released to the surroundings
(exothermic)
Calculation:
- Step one: Add together all the bond energies for all the bonds in the reactants – this is
the ‘energy in’
- Step two: Add together the bond energies for all the bonds in the products – this is the
‘energy out’
- Step three: Calculate the energy change (energy in – energy out)
Describe the release of heat energy by burning fuels:
- Fuel: a material (e.g. wood, coal, gas, oil) that can be burned to produce heat, light or
power
- The fossil fuels are coal, oil and natural gas
- They are fuels because they release heat energy when burned
- They are fossil fuels because they were formed from the remains of living organisms
millions of years ago
- Combustion: a chemical process in which a substance reacts rapidly with oxygen and
gives off heat
- The heat that is used to burn fossil fuels cause molecules of carbon and hydrogen to
react and produce large amount of energy
Hydrogen:
- Hydrogen is often seen as an environmentally-friendly alternative to fossil fuels
There are two ways in which hydrogen is used to power cars:
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