C6 - Energy changes in chemical reactions
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In chemical reactions energy cannot be
created or destroyed only transferred
Depending on energy transfer chemical reactions are either
exothermic or endothermic
Exothermic reactions get
hotter as energy from reacting chemicals is transferred to the surrounding which increases temperature. The energy given out can be used to keep the reaction going so they don’t stop until they run out of reactants.
examples of exothermic reactions
Combustion of fuels Acid-base neutralization Displacement reactions Respiration in cells
Endothermic reactions
get colder as the energy from surroundings are transferred to reacting chemicals causing temperature of surroundings to decrease. Endothermic reactions need a constant energy supply to keep the reaction going.
examples of endothermic reactions
Thermal decomposition Photosynthesis Cooking
In exothermic reactions chemical energy stored in reactants gets converted to heat energy so
the products have less chemical energy than the reactants and the difference is the heat released.
In endothermic reactions heat energy gets converted to chemical energy so
the products have more chemical energy than the reactants.
2 requirements for a reaction to take place successfully
• reacting particles must collide 2. collisions must have more than enough activation energy
A molecule of ethane and a molecule of iodine react. What needs to happen for the reaction to occur.
The ethane and iodine molecules must collide. They must collide with more energy than the activation energy.