Studied by 0 peopleexothermic reaction
During a(n) ________, more energy is energy is given out when new bonds are made than the energy taken in to break bonds.
symbol ΔH
The ________ (delta H) is used to show the change in heat energy.
new bonds
More energy is released when ________ are formed than energy required to break the bonds in the reactants.
H
________ is the symbol for enthaply, which is a measure of the total heat of reaction of a chemical reaction.
chemical reaction
During a(n) ________ there is always an energy change.
endothermic reaction
Therefore a(n) ________ has a positive ΔH value, which is shown on the energy level diagrams and in calculations.
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.
Give an example of a type of reaction that is exothermic.
Combustion & Neutralisation
Give an example of an endothermic reaction
Thermal decomposition & Photosynthesis
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.
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
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
If the energy change of a reaction is negative, is the reaction exothermic or endothermic?
Exothermic Energy has been lost to the surroundings
Fill in the gap: ‘Fuels are burned to release ____ ____’
Heat energy
Which colourless gas can be used as a fuel?
Hydrogen
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).
What are the advantages of fuel cells?
No pollution produced
Produce more energy than an alternative fuel like petrol
Continuous process as long as fuel is supplied
Note
Flashcard