What is the conservation of energy principle?
Energy is conserved in chemical reactions. The amount of energy in the universe at the end of a chemical reaction is the same as before the reaction takes place
What is an exothermic reaction? Give examples.
A reaction where energy is transferred to the surroundings so that the surroundings temperature increases - combustion, oxidation reactions and neutralisation (acid + alkali) reactions. Negative sign of energy change.
What is an endothermic reaction? Give examples
A reaction where energy is taken in from the surroundings so the surroundings
temperature decreases - thermal decomposition, reaction of citric acid and sodium hydrogencarbonate. Positive sign of energy change.
What is activation energy?
Minimum amount of energy particles need to react
What is a reaction profile?
Reaction profile is a graph which shows the relative energies of reactants and product, as well as activation energy of the reaction.
What occurs in a chemical reaction in terms of bond energies? Describe exothermic and endothermic reactions in terms of bond breaking/forming.
Energy is supplied to break bonds and energy is released when bonds are made;
exothermic - energy released from forming bonds is greater than that needed to break the bonds;
endothermic - energy needed to break bonds is greater than energy released making them
What is the equation to find enthalpy (chemical energy involved in the reaction) change in terms of bond energies?
Energy of reaction = sum of bonds broken - sum of bonds made
How can you improve the accuracy of the polystyrene cup experiment when measuring temperature change?
Use a lid to reduce heat loss to the air.
• Use more insulation (e.g. cotton wool or extra cup) to keep heat in.
Describe how to carry out the polystyrene cup practical to measure a temperature change.
1️⃣ Measure a fixed volume of acid (or solution) with a measuring cylinder into a polystyrene cup.
2️⃣ Record the starting temperature using a thermometer.
3️⃣ Add a measured amount of alkali (or reactant) and stir.
4️⃣ Record the highest or lowest temperature reached during the reaction. Can by improved by using Use a digital thermometer, repeat experiment to calculate a mean, add extra insulation.
