energetics (paper 1) 55-57
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what is meant by the term exothermic reaction
a reaction that gives out energy to surroundings, usually in the form of heat and shown by a rise in temperature
is bond breaking an exothermic or endothermic reaction
endothermic
if a reaction is exothermic does the temperature rise or fall
rise
give 2 examples of exothermic reactions
• condensing steam to water • adding potassium to water
what is meant by the term endothermic reaction
a reaction that takes energy in from the surroundings, shwon by a fall in temperature
what is the change in energy called
the enthalpy change
what is meant by the term enthalpy change
the overall change in energy in a reaction is called the enthaply change
what is the symbol for enthalpy change
ΔH
what are the units for enthalpy change (ΔH)
kJ/mol
what is the value of an enthalpy change like if the reaction is EXOthermic
the value will be negative because the reaction gives OUT energy
what is the value of an enthalpy change like is the reaction is ENDOthermic
the value will be positive beacuse the reaction takes IN energy
what is the equtation for enthalpy change (just energy release overall = Q)
Q = mass of liquid heated x specific heat capacity x change in temperature
what is the equation for energy release per mole (enthalpy change per mole)
Q/mol
what are the different types of enthalpy change
• enthalpy of combustion • enthalpy of displacement • enthalpy of neutralisation • enthalpy of dissolving
what is the term for the process used to measure enthalpy change
calorimetry
which three types of calorimetry are have the same method
• enthalpy of displacement • enthalpy of neutralisation • enthalpy of dissolving
which type of calorimetry has a different method
enthalpy of combustion
what are the problems with normal calorimetry
• heat loss to the surroundings, from the can = insulated the can, using a lid • incomplete combustion resulting in a build up of soot (insulator) • alcohols are volatile so mass can be lost as soon as lid is removed • activation energy can be too high or too slow so bond energy calculations must be used instead
desribe the calorimetry method for dissolving, displacement and neutralisation
• put 25cm^3 of acid and base into seperate beakers • place the beakers in a waterbath to 25°C until they are the same temperature • add acid and base into insulated, polystyrene cup with a lid with a thermometer • take the temperature of the mixture every 30sec and record the highest temperature • repeat 3 more times
describe the calorimetry method for combustion
• weight the spirit burner, with its lid on, on the balance and record the mass • measure out 100cm^3 water and pour into the calorimeter (copper can) • set up the equipment as shown in the diagram by clamping the calorimeter a good hieght above the spirit burner • record the starting temperature of the water • light the burner and stir the water, monitoring the temperature until 100°C • estinguish the flame and re-weigh the spirit burning • calculated the energy change and the enthalpy change