When measuring enthalpy changes, why does it not matter that the thermometer measures temperature in °C instead of K?

Because the value of the temperature change is exactly the same in °C and in K.

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How is the temperature change of the surroundings determined?

By subtracting the initial temperature from the final temperature.

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What 3 quantities are used to calculate the energy change of the surroundings?

1The mass of the surroundings.

2The specific heat capacity of the surrundings.

3The temperature change of the surroundings.

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Name the apparatus used to experimentally determine the enthalpy change of combustion of a fuel.

A calorimeter

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What are the steps for determining the enthalpy change of combustion (ΔHc) of a fuel using a combustion calorimeter?

  1. Weigh a sample of the fuel.
  2. Place the fuel sample underneath a metal canister (calorimeter) containing a known mass of water.
  3. Record the initial temperature of the water.
  4. Burn the fuel sample, allowing the heat to transfer to the water in the calorimeter.
  5. Measure the maximum temperature change of the water using a thermometer.
  6. Calculate the heat energy transferred to the water using the equation q = mcΔT.
  7. Calculate the enthalpy change of combustion (ΔHc) using the equation ΔHc​=−nq​.

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Give 3 possible reasons for the difference between the experimental and data book values of ΔHc?

1Heat loss to the surroundings.

2Incomplete combustion.

3Evaporation of the fuel.

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What is the sign of ΔHc for the combustion of any fuel?

Negative, indicating an exothermic reaction.

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What is the purpose of using plastic cups made of polystyrene foam in measuring enthalpy changes of reactions in solution?

Polystyrene foam is a good insulator so it reduces heat loss to the surroundings through their sides.


Polystyrene also has a low specific heat capacity so it absorbs very little heat.

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How can you use a cooling curve to determine a more accurate value of ΔHneut?

By drawing a straight line of best fit through the graph points after mixing and extrapolating back to the time of mixing; this gives a more accurate estimate of the maximum temperature reached.

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How is the mass of the surroundings determined in an experment to measure ΔHneut?

Assume the density of dilute solutions is 1 g cm-3.

The mass (in grams) of the surroundings is equal to the total volume of the solution (in cm3) after acid and alkali are combined.

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What is the equation that links energy change (q) to mass (m), specific heat capacity (c), and temperature change (ΔT)?

q = mcΔT


q = energy change (J)

m = mass (g)

c = specific heat capacity (J g-1 K-1)

T = temperature change (K)

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What is the equation that links enthalpy change (ΔH) to energy change (q), and number of moles (n)?

ΔH =−nq​


ΔH = enthalpy change (kJ mol-1)

q = enthalpy change (kJ)

n = number of moles of substance (mol)

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