Physical Chemistry - Energetics
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what is an exothermic reaction?
a chemical reaction in which heat energy is given out
what is an endothermic reaction?
a chemical reaction in which heat energy is taken in
what does calorimetry allow?
for the measurement of the amount of energy transferred in a chemical reaction to be calculated
how would you do a calorimetry experiment for a displacement/dissolving/neutralisation reaction?
magnesium displacing copper from copper(II) sulfate: - 50 cm³ of copper(II) sulfate is measured and transferred into a polystyrene cup - the initial temperature of the copper sulfate solution is measured - magnesium is added and the maximum temperature is measured - temperature rise is then calculated
why is the cup polystyrene in a calorimetry experiment?
polystyrene is an insulator which reduces heat loss
how would you do a calorimetry experiment for a combustion reaction?
ethanol being burnt in a small spirit burner: - initial mass of the ethanol and spirit burner is measured - 100cm³ of water is transferred into a copper container and the initial temperature is measured - the burner is placed under the copper container and lit - the water is stirred constantly with the thermometer until the temperature rises by a set amount - the flame is extinguished and the maximum temperature of the water is measured - the burner and the remaining ethanol is reweighed
how would you calculate heat energy change?
amount of energy transferred = mass x specific heat capacity x temperature rise Q = mcΔT
how do you calculate the molar enthalpy change?
molar enthalpy change = amount of energy transferred (Q)/number of moles