Year 8 Chemistry: Heat and Reaction Rates PDF

Heat can speed up reactions Year 8 Chemistry  the rate of a reaction can be sped up or slowed down. Learning factors that can increase the rate of a reaction include increasing the Objectives surface area of the reactants,...

Heat can speed up reactions Year 8 Chemistry  the rate of a reaction can be sped up or slowed down. Learning factors that can increase the rate of a reaction include increasing the Objectives surface area of the reactants, increasing the temperature and concentration of substances, and adding a suitable catalyst. Key Words Rate of reaction: the speed at which a chemical reaction occurs; reactants become products Collision Theory: a theory stating that the particles involved in a chemical reaction must collide in order to react Concentration: the number of active molecules in a set volume of solution Catalyst: a substance that increases the rate of a chemical reaction without undergoing any permanent chemical change Enzyme: a chemical that helps make chemical reactions happen; a type of catalyst All reactions happen at a certain speed Rate of reaction: the rate at which the reactants become products in a reaction  All chemical reactions rely on particles interacting For the reaction to happen, the correct particles of reactants must collide with each other to make a product. Collision theory: is the theory stating that particles involved in a chemical reaction must collide with each other to react. The rate at which the particles collide is the rate at which the chemical reaction occurs You can change the rate that a reaction happens by changing how the particles interact Option 1: Increase the number of collisions by changing the temperature To speed up a reaction: + heat (thermal energy) also The particles are increases kinetic MORE likely to collide. energy (particles will move more). To slow down a reaction: - heat (thermal energy) The particles are LESS decreases the kinetic likely to collide. energy (particles move slower). Option 2: change the concentration (the number of particles you have in a small area) To speed up the reaction: Increase the More collisions mean concentration  means reaction happens faster. particle are more likely to collide. To slow down the reaction: decrease the Less collisions mean concentration  the reaction happens slower. particles are more likely to not collide. Option 3: change the surface area - for solids To speed up the reaction: Smaller reactant pieces have a larger total surface area  This means that the reaction The reactant particles have a should be faster greater chance of interacting with each other. To slow down the reaction: Larger reactant pieces have a smaller total This means the reaction will surface area  The reactant be slower particles have less chance of interacting with each other. Option 4: add catalysts to make the reaction more likely. A catalyst is a substance that increases the rate of a chemical reaction without undergoing any permanent chemical change. In living things, a type of catalyst called an enzyme does this. Enzymes act like landing strips for reactants, allowing the chemicals to collide with each other more easily. Enzymes are very 'fussy' and only work with one type of reactant and so will only catalyse one reaction each. Examples of Enzymes Digestive system – enzymes help break down food Fruit – enzymes are responsible for ripening fruit So if you change the rate or reaction – does this mean you have more or less product?