During a(n) ________, more energy is energy is given out when new bonds are made than the energy taken in to break bonds.
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symbol ΔH
The ________ (delta H) is used to show the change in heat energy.
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new bonds
More energy is released when ________ are formed than energy required to break the bonds in the reactants.
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H
________ is the symbol for enthaply, which is a measure of the total heat of reaction of a chemical reaction.
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chemical reaction
During a(n) ________ there is always an energy change.
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endothermic reaction
Therefore a(n) ________ has a positive ΔH value, which is shown on the energy level diagrams and in calculations.
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What do the terms exothermic and endothermic mean?
Endothermic - a reaction that takes in heat energy from the surroundings. Exothermic - a reaction that gives out energy to the surroundings.
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Give an example of a type of reaction that is exothermic.
Combustion & Neutralisation
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Give an example of an endothermic reaction
Thermal decomposition & Photosynthesis
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In terms of bond energies, what happens during a chemical reaction? Describe exothermic and endothermic reactions in terms of bonds breaking / making
Energy is needed to break bonds and is released when bonds are made. Exothermic: Energy released from making bonds is greater than the energy used to break bonds. Endothermic: Energy required to break bond is greater than the energy released when making bonds.
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What is a reaction profile?
A graph which shows the relative energies of reactants and products, as well as the activation energy of the reaction
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How can the energy change of a reaction be calculated from bond energies?
Energy change (kJ mol-1) = Total energy of bonds broken - total energy of bonds made
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If the energy change of a reaction is negative, is the reaction exothermic or endothermic?
Exothermic Energy has been lost to the surroundings
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Fill in the gap: ‘Fuels are burned to release ____ ____’
Heat energy
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Which colourless gas can be used as a fuel?
Hydrogen
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What is a fuel cell?
A cell that continually produces a voltage as long as it is supplied with oxygen and a fuel (like hydrogen).
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What are the advantages of fuel cells?
No pollution produced
Produce more energy than an alternative fuel like petrol
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