chem - rates of reaction + energy changes (7)

• When hydrochloric acid and sodium thiosulphate react, the solution turns cloudy.
• The rate of a chemical reaction can be measured by altering the concentration of sodium thiosulphate and measuring the time it takes for the solution to turn fully opaque.
• The rate of a chemical reaction is measured in terms of the amount of reactant or product consumed per unit time.
• To increase the rate of a chemical reaction, the frequency or energy of collisions can be increased.
• The rate of a chemical reaction can be increased by increasing the temperature, pressure, concentration, or adding a catalyst.
• The steeper the curve, the greater the increase or decrease in rate.
• Catalysts are substances that speed up chemical reactions without being used up and have the same mass at the end of the reaction.
• Enzymes are biological catalysts found in yeast.
• Neutralisation reaction is exothermic.
• Displacement is an exothermic or endothermic reaction.
• Precipitation is an exothermic reaction.
• Exothermic reactions transfer energy to the surroundings so the temperature of the surroundings increases.
• Endothermic reactions take in energy so the temperature of the surroundings decreases.
• During a chemical reaction, energy must be supplied to break bonds in the reactants and energy is released when bonds in the products are formed.
• Energy taken in to break bonds minus energy released to form bonds equals overall energy change.
• Activation energy is the minimum amount of energy that particles must have to react.
• Reaction profiles can be used to show the relative energies of reactants and products, the activation energy and the overall energy change of a reaction.
• For the exothermic diagram, the products have less energy than the reactants, because the energy has been released to the surroundings.
• For the endothermic diagram, the reactants have less energy than the products, because the energy has been taken in from the surroundings.