Chemical Reaction Rates (OCR) PDF

THE RATE OF CHEMICAL REACTIONS  The bonds between the atoms in the reactants must first be broken. – For this to occur energy must always be absorbed New bonds form as the products are created – Energy is always released as this happens  COLLISION THEORY For a chemi...

THE RATE OF CHEMICAL REACTIONS  The bonds between the atoms in the reactants must first be broken. – For this to occur energy must always be absorbed New bonds form as the products are created – Energy is always released as this happens  COLLISION THEORY For a chemical reaction to occur, the particles involved must collide with each other. The collisions must be with sufficient energy to overcome the activation energy ‘barrier’. The rate of reaction (how quickly the reaction occurs) depends on the number of energy sufficient collisions per time. Activation energy:The minimum amount of energy that particles need to react.  Collision Model Molecules must collide in order for a reaction to occur. What factors affect the rate of collisions?  There are four main ways in which reaction rates can be increases: – Increase the surface area of solid reactants (crush) – Increase the concentration of the reactants – Increasing the temperature of the reactants – Adding a catalyst Explain how each of these factors can increase the rate of reaction. As the concentration of the reactants goes up the distance between the molecules becomes less. With less distance to travel the time between collisions becomes less  Temperature The faster the molecules move the less time it take for them to reach another molecule. Higher the temperature, the faster the reaction.  The effect of catalyst Many reactions occur more rapidly in the presence of particular elements or compounds. These substances, known as catalysts, are not consumed during the reactions, they just help it along They often work by lowering the activation energy. Enzymes are biological catalysts.  Catalyst (transition metals) How to make a reaction occur… Activation Energy: minimum amount of energy needed to start a chemical reaction Rates of Chemical Reactions Surface Area – The more surface area that is exposed, the faster the reaction will occur- Example- chewing your food breaks it into smaller pieces with more surface area. It takes less time to digest your food. Temperature- The higher the temperature the faster the particles move. This means they interact more often and have more energy. Example: Storing Milk in the fridge slows down reactions to stay fresher longer.  More ways to control a reaction Concentration- the amount of substance in a given volume. Increasing the concentration allows for more particles to react. Catalyst- material that increases the rate of reaction by lowering the activation energy Enzymes- Produced in your body that acts as catalysts. Inhibitor- material used to decrease the rate of a reaction. Example: antioxidants