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Science C2 Topic 5

Edexcel GCSE additional science chemistry: chemical reactions

What are exothermic reactions? Reactions in which more energy is released making new bonds for the products than is needed to break the bonds of the reactants- so energy is released
What are some examples of exothermic reactions? Combustion of fossil fuels, explosions, bond making
What are endothermic reactions? Reactions in which more energy is needed to break the bonds of the reactants than is released by the making of new bonds for the products- so energy is absorbed
What are some examples of endothermic reactions? Photosynthesis, bond breaking
What is the rate of a reaction? The speed at which it takes place
What are examples of very fast and slow reactions? Very fast: explosions, combustion Slow: rusting of iron
What is the collision theory? The theory that for a reaction to occur, there must be successful collisions between the reactants
Why are not all collisions successful? If the particles collide with low energy
What are rates of reaction affected by? * higher temperature increases the speed of particles so they are more likely to collide & with more energy * larger surface area of a solid allows more collisions at one time * higher concentration of solution increases amount of particles
What is a catalyst? A substance that speeds up the rate of a chemical reaction without being changed by the reaction
What are the advantages of using a catalyst? Chemical reactions can be done at lower temperatures and pressures so it is cheaper and safer
What are catalytic converters and what are they made out of? devices fitted to car exhausts that reduce the release of pollutants in exhaust gases- they combine CO and urburnt fuel with oxygen- they are made out of transition metals e.g platinum, palladium, rhodium in a honeycomb structure with a large surface area
What conditions do catalytic converters work best in? High temperatures- faster rates of reaction
Created by: 11043