Year 12 IB Chemistry
Targeted Skills Worksheet
Measuring Energy Changes Worksheet
Question 1
Define:
a) Standard enthalpy change of reaction
b) Standard enthalpy change of combustion
c) enthalpy change of neutralisation
d) enthalpy change of solution
Question 2
Deduce from the enthalpy level diagrams below if the reaction is:
• Exothermic
• Endothermic
• Reactants lower energy than products?
• Products lower energy than reactants?
• H positive or negative?
Question 3
Calculate the activation energy for the reverse reaction given the following enthalpy level diagrams:
x
y
Question 4
Use the following experimental data to determine the enthalpy change of combustion of ethanol
(C2H5OH) given that the specific heat capacity of water is 4.18 J g-1 ℃-1.
Mass of water = 150.00g
Initial temperature of water = 19.5℃
Maximum temperature of water = 45.7℃
Initial mass of spirit burner = 121.67g
Final mass of spirit burner = 120.62g
Question 5
Consider the following experiment. 100.0 cm 3 of 1.00 mol dm-3 potassium hydroxide solution is
measured out and poured into a polystyrene cup and the temperature of the potassium hydroxide
solution was measured. Then 120.0 cm 3 of 1.00 mol dm-3 hydrochloric acid are measured out and the
initial temperature was measured. The hydrochloric acid was in excess to make sure that all the
potassium hydroxide reacted. The hydrochloric acid was then poured into the polystyrene cup and the
mixture stirred rapidly. The maximum temperature was recorded.
The results of this experiment:
Initial temperature of potassium hydroxide solution = 19.7 ℃
Initial temperature of hydrochloric acid = 19.7℃
Maximum temperature reached = 25.9℃
Use these data to determine the enthalpy change of neutralisation.
Year 12 IB Chemistry
Targeted Skills Worksheet
Question 6
100.0 cm3 of water are measured out and poured into a polystyrene cup and the temperature of the
water was measured. Then 5.20 g of ammonium chloride are measured out. The ammonium chloride
was added to the water and the solution stirred vigorously until all the ammonium chloride had
dissolved. The minimum temperature was recorded.
The results of this experiment are:
Initial temperature of water = 18.3℃
Minimum temperature = 15.1 ℃
Use the experimental data to determine the enthalpy change of solution of ammonium chloride.
Question 7
The following experiment is used to
determine the enthalpy change of reaction
for:
Zn(s) + CuSO4(aq) → ZnSO4(aq) + Cu(s)
50.0 cm3 of 0.200 mol dm-3 copper (II)
sulfate solution are placed in a polystyrene
cup. The temperature was recorded every
30s. At 80s, 1.20 g of powdered zinc are
added. The
mixture was stirred
vigorously and the temperature recorded
every half minute for several minutes. The
results obtained were then plotted to give the
graph shown in the figure below.
Use these data to determine the enthalpy
change for this reaction.
Question 8
A student titrated an ethanoic acid solution,
CH3COOH (aq), against 50.0 cm3 of 0.995 mol dm–
3
sodium hydroxide, NaOH (aq), to determine its
concentration.
The temperature of the reaction mixture was
measured after each acid addition and
plotted against the volume of acid.
a)
b)
c)
d)
Determine the maximum temperature
reached in the experiment by analysing
the graph.
Calculate the concentration of ethanoic
acid, CH3COOH, in mol dm–3.
Determine the heat change, q, in kJ, for
the neutralization reaction
between ethanoic acid and sodium
hydroxide.
Assume the specific heat capacities of the
solutions and their densities are those of
water. Calculate the enthalpy change, ΔH,
in kJ mol–1, for the reaction between
ethanoic acid and sodium hydroxide.
Year 12 IB Chemistry
Targeted Skills Worksheet
Question 9
Impurities cause phosphine to ignite spontaneously in air to form an oxide of phosphorus and water.
200.0 g of air was heated by the energy from the complete combustion of 1.00 mol phosphine.
Calculate the temperature rise using section 1 of the data booklet and the data below.
Standard enthalpy of combustion of phosphine,
Specific heat capacity of air = 1.00 J g−1 K−1
Question 10
In an experiment, 2.50 g of solid sodium hydroxide was dissolved in 50.0 cm3 of water. The
temperature rose by 13.3 ℃. Calculate the standard enthalpy change, in kJ mol-1, for dissolving one
mole of solid sodium hydroxide in water.
NaOH(s) → NaOH(aq)
Question 11
When ammonium chloride, NH4Cl(aq), is added to excess solid sodium carbonate, Na2CO3(s), an
acid–base reaction occurs. Bubbles of gas are produced and the solid sodium carbonate decreases in
mass.
a) Sketch and label an enthalpy level diagram for this reaction.
b) Deduce whether the reactants or the products are more energetically stable, stating your
reasoning.
c) When 5.35 g ammonium chloride, NH4Cl(s), is added to 100.0 cm3 of water, the temperature
of the water decreases from 19.30 °C to 15.80 °C. Determine the enthalpy change, in kJ
mol−1, for the dissolving of ammonium chloride in water.