# Rates of reaction

• Created by: Holly45
• Created on: 13-03-15 17:40

## Energy transfer

• exothermic reaction is when energy is transferred to its surroundings usually in the form of heat
• neutralisation reactions are also exothermic
• an endothermic reaction is when energy is taken in from its surroundings
• thermal decomposition is an endothermic reaction
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## Collision theory and catalysts

• increasing temperature causes faster collisions
• the minimum amount of energy needed by the particles to react is known as the activation energy
• a catalyst speeds up a reaction without being changed
• different reactions need different catalysts
• catalysts are expensive
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## Collision theory

• more collisions will increase the rate of reaction
• an increase in temperature makes the particles move quicker
• a more concentrated solution means more reactant particles and water molecules colliding
• in a gas, increasing the pressure means the particles are squeezed together so more frequent collisions will occur
• a larger surface area means more frequent collisions
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## Experiments

THIOSULFATE AND HCL:

• 2 chemicals are both clear solutions
• react together to form a yellow precipitate of sulphur
• higher temperature quicker reaction
• black mark to disappear through the cloudy sulphur and timing how long it takes

HYDROCHLORIC ACID AND MARBLE CHIPS

• gas syringe and take readings at regular intervals
• repeat the experiment with exactly the same volume of acid, and exactly the same mass of marble chips but more crushed up
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## Measuring the rate of reaction

• can be measured by either how quickly the reactants are used up or how quickly the products are formed
• rate of reaction = amount of product formed/reactant used (divided by) time

PRECIPITATION:

• measure how long it takes for a mark to dissapear
• clouds the solution
• people disagree the exact point at which the cross disappears

CHANGE IN MASS:

• the quicker the reading on the balance drops the faster the reaction
• most accurate

VOLUME OF GAS GIVEN OFF:

• the more gas given off during a given time interval, the faster the reaction
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