Energy Changes
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Describe how energy is transferred to or from the surroundings during a chemical reaction
Endothermic - takes in energy from the surroundings Exothermic - transfers energy out to the surroundings
Explain exothermic and endothermic reactions on the basis of the temperature change of the surroundings and give examples of everyday uses
Endothermic - surroundings fall in temperature, thermal decompositions Exothermic - surroundings rise in temperature, combustion and neutralisation (acid + alkali)
Required practical 10: investigate the variables that affect temperature changes in reacting solutions
Method: Put HCl and sodium hydroxide in separate beakers Place beakers in 25℃ until they are at the same temperature Add HCl followed by NaOH to polystyrene cup with lid Take temperature of mixture every 30 secs and record highest temp Repeat steps 1-4 with different concentrations of of HCl Independent - Dependent - Control -
Describe what the collision theory is and define the term activation energy
Collision theory - For a chemical reaction to occur, the reactant molecules must collide with enough energy Activation energy - minimum amount of energy needed that reactants need to react
HT ONLY: Explain the energy changes in breaking and making bonds and calculate the overall energy change using bond energies
Bond breaking - Endothermic Bond Forming - Exothermic Overall = total energy needed - total energy released energy to break bonds when forming new bond change