Calorimetry lab
Measure temperature changes for neutralisation, dissolving, displacement and burning alcohols, correct for heat loss, calculate ΔH from q = mcΔT and see it on an energy profile.
Find this activity in your course
Learning objectives
- describe the term exothermic as a process or chemical reaction which transfers energy, often in the form of heat, to the surroundings and may be detected by an increase in temperature, e.g. the reaction between sodium hydroxide and hydrochloric acid
- describe the term endothermic as a process or chemical reaction which takes in energy, often in the form of heat, from the surroundings and may be detected by a decrease in temperature, e.g. the dissolving of ammonium nitrate in water.
- describe the meaning of enthalpy change in terms of exothermic (∆H negative) and endothermic (∆H positive) reactions
- represent energy changes by energy profile diagrams, including reaction enthalpy changes and activation energies (see also 10(c), 10(d))
- construct and interpret an energy profile diagram, in terms of the enthalpy change of the reaction and of the activation energy (see also Section 7)
- explain and use the terms: — enthalpy change of reaction and standard conditions, with particular reference to: formation; combustion; neutralisation
- calculate enthalpy changes from appropriate experimental results, including the use of the relationship: heat change = mc∆T
- Enthalpy Changes and Energy Profiles
- Calorimetry (q = mcΔT)
Neutralisation: HCl + NaOH in a polystyrene cup with a lid. The reagents are mixed at 120 s; at 0 s the thermometer reads 25.0 °C.
- Alcohol burned, Δm
- — g
- ΔT
- — °C
- q = mcΔT
- — J
- n
- — mol
- ΔH = −q/n
- — kJ/mol
Try this
0 of 4 doneMeasure ΔH of neutralisation, reading the thermometer for the full 10 minutes. (not done yet)
The solution warms, so the reaction gives out heat and ΔH = −q/n is negative. The line extrapolated back to the moment of mixing corrects for heat lost while the reaction happened.
Repeat the neutralisation with acid and alkali twice as concentrated. (not done yet)
Twice as much water forms in the same mass of solution, so ΔT doubles, but ΔH per mole of water stays the same.
Dissolve ammonium nitrate, then sodium hydroxide, and compare the sign of ΔH. (not done yet)
Ammonium nitrate takes in heat from the water (endothermic, ΔH positive); sodium hydroxide gives out heat (exothermic, ΔH negative).
Burn two different alcohols and compare their ΔH of combustion per mole. (not done yet)
Each extra CH₂ makes ΔH of combustion about 650 kJ/mol more negative in the data book. Your values are smaller because heat escapes to the air and the can.