5.1 Energetics

Question 1d

Marks: 6

d)

Define the term enthalpy of formation, ΔH_f , and state the standard conditions.

Key Concepts

Question 2a

Marks: 2

a)

Define the term enthalpy change of reaction, ΔH_r.

Key Concepts

Question 2b

Marks: 3

b)

The equations below can be identified as any of the following enthalpy changes. Identify the enthalpy change for each reaction.

Enthalpy of reaction, ΔH_r
Enthalpy of formation, ΔH_f
Enthalpy of combustion, ΔH_c
Enthalpy of neutralisation, ΔH_neut

C₂H₅OH (l) + O₂ (g) → CO₂ (g) + H₂O (l) …………………………………………

CaSO₃ (s) → CaO (s) + SO₂ (g) ……………………………………………

HCl (aq) + NaOH (aq) → NaCl (aq) + H₂O (l) …………………………………………

Key Concepts

Question 2c

Marks: 2

c)

Hydrochloric acid, HCl (aq), and sodium hydroxide, NaOH (aq), react as follows

HCl (aq) + NaOH (aq) → NaCl (aq) + H₂O (l) ΔH_r = -57.9 kJ mol^-1

Determine the enthalpy change, in kJ, when 25 cm³of 0.5 mol dm^-3 hydrochloric acid reacts with 25 cm³of 0.5 mol dm^-3 sodium hydroxide. Give your answer to 2 decimal places.

Key Concepts

Question 3a

Marks: 3

a)

A student set up apparatus for a calorimetry experiment as shown below.

Suggest suitable materials for the lid and cup. Justify your answer.

IB Chem 5.1 SQ E Q3a

Key Concepts

Question 3b

Marks: 3

b)

The student added excess zinc powder to the cup with 50.0 cm³of 1.0 mol dm^-3 copper(II) sulfate solution in a calorimeter. The reaction equation was as follows:

Zn (s) + CuSO₄(aq) → ZnSO₄(aq) + Cu (s)

The maximum temperature rise was 22.6 ^oC. Using section 1 of the data booklet, determine the enthalpy of reaction, in kJ. Give your answer to 2 significant figures.

Calculate the energy change, q …………………………

Calculate the number of moles of copper(II) sulfate solution ………………

Calculate the enthalpy change of the reaction …………………

Key Concepts

Question 3c

Marks: 2

c)

Another calorimetry experiment was set up to determine the enthalpy of combustion for ethanol.

6-3

Define standard enthalpy of combustion, ΔH_c.

Key Concepts

Question 3d

Marks: 2

d)

0.61 g of ethanol, C₂H₅OH, was burned in a spirit burner and used to heat 100 cm³ of water in a copper calorimeter. The temperature of the water rose by 40 ^oC.

i)

Using section 1 and 2 in the data booklet determine the energy, in joules, for this reaction.

ii)

Convert your answer to part (i) into kilojoules.

Key Concepts

Question 3e

Marks: 3

e)

Calculate the enthalpy change for the combustion of ethanol.

Determine the moles of ethanol ………………………..

Determine the overall enthalpy change …………………………..

Key Concepts

Question 4a

Marks: 1

a)

4.00 g of powdered iron was reacted with 25.0 cm³ of 2.00 mol dm⁻³ copper(II) sulfate solution in an insulated beaker. Temperature was plotted against time.

5-1-ib-sl-sq-easy-q4a-calorimetry

Estimate the time at which the powdered iron was added to the beaker.

Key Concepts

Question 4b

Marks: 3

b)

A student added point Y to the graph.

i)

State what point Y indicates on the graph.

ii)

Assuming there is no heat loss in the experiment and the heat change is instantaneous, using the graph, determine the total temperature change.

Key Concepts

Question 4c

Marks: 1

c)

Explain why the student has recorded the temperature of the copper sulfate solution for a period of time before adding the iron powder.

Key Concepts

Question 4d

Marks: 1

The student used the equation q = mcΔT to calculate the enthalpy change for the reaction that took place in the beaker. State the value that the student should use for m.

Key Concepts