IB Chemistry HL Reactivity 1: What drives chemical reactions? questions

Exam-style multiple choice and written questions with full markschemes. Check multiple choice answers straight away, or type, photograph or draw a written answer and get it marked.

Type

Multiple choice Written

Difficulty

Easy Medium Hard

Question 1

Paper 2Medium3 marks

Citric acid solution is mixed with solid sodium hydrogencarbonate in an insulated cup. Treat the reacting chemicals as the system and the solution and cup as the surroundings. Figure 1 shows the measured temperature of the solution before and after mixing; the reagents are mixed immediately after the reading at $t=0$

(a)

Determine the temperature change of the surroundings from immediately before mixing to the lowest recorded value. Include the sign.

[1]

(b)

Hence classify the reaction and explain the temperature change, referring to energy transfer, particle kinetic energy and conservation of energy.

[2]

Question 2

Paper 2Easy4 marks

Ethanol, C₂H₅OH(l), is used as a fuel. Its complete combustion produces carbon dioxide and liquid water. The standard enthalpies of formation at 298 K are:

Substance	ΔH°f / kJ mol⁻¹
C₂H₅OH(l)	−277.7
O₂(g)	0
CO₂(g)	−393.5
H₂O(l)	−285.8

(a)

Write the balanced equation for the complete combustion of ethanol, including state symbols.

[2]

(b)

Using the equation in (a) and the equation for enthalpies of formation in the data booklet, determine the standard enthalpy change for the combustion of 1 mol of ethanol. Give your answer in kJ mol⁻¹.

[2]

Question 3

Paper 2Easy8 marks

A student compares the air supply to two identical burners, each supplied with methane, CH₄, at the same rate. Figure 1 is a schematic diagram; the side arrows indicate the relative air supply to each burner.

(a)

Using Figure 1, identify which burner is more likely to undergo incomplete combustion. Give one reason based on the figure.

[2]

(b)

For burner B, write a balanced equation for incomplete combustion of methane in which carbon monoxide and water are the products. State symbols are not required.

[2]

(c)

Ethanol, C₂H₅OH, burns with a restricted oxygen supply to form solid carbon and water. Write a balanced equation for this reaction. State symbols are not required.

[2]

(d)

State one health risk of carbon monoxide and suggest one change that would reduce the likelihood of carbon monoxide forming or accumulating.

[2]

Question 4

Paper 2Medium7 marks

A pilot plant produces bioethanol from glucose in crop biomass. Figure 1 shows a simplified carbon pathway for one batch. The fermentation equation is:

\ce{C6H12O6 -> 2C2H5OH + 2CO2}

Use relative atomic masses from the data booklet where needed.

(a)

Write a balanced equation for photosynthesis in plants.

[1]

(b)

Use the fermentation equation and Figure 1 to calculate the theoretical mass of ethanol and the percentage yield for this batch. Give the mass in kg and the percentage yield to three significant figures.

[3]

(c)

Using Figure 1, explain why the ethanol can be considered a renewable fuel.

[2]

(d)

State one reason why Figure 1 alone does not establish that using this bioethanol is carbon neutral.

[1]

Question 5

Paper 2Medium7 marks

Calcium carbonate decomposes on heating according to the reaction

\ce{CaCO3(s) -> CaO(s) + CO2(g)}.

The standard entropy values and standard enthalpy change for this reaction are given below. Figure 1 shows how $\Delta_\mathrm r G^\circ$ varies with temperature.

Substance or quantity	Value
$S^\circ(\ce{CaCO3(s)})$	$92.9\ \mathrm{J\,K^{-1}\,mol^{-1}}$
$S^\circ(\ce{CaO(s)})$	$39.8\ \mathrm{J\,K^{-1}\,mol^{-1}}$
$S^\circ(\ce{CO2(g)})$	$213.7\ \mathrm{J\,K^{-1}\,mol^{-1}}$
$\Delta_\mathrm r H^\circ$	$+178.3\ \mathrm{kJ\,mol^{-1}}$

(a)

Calculate $\Delta_\mathrm r S^\circ$ for the reaction. Include the sign and units.

[2]

(b)

Using Figure 1, determine the approximate temperature at which $\Delta_\mathrm r G^\circ$ changes sign. State whether the forward reaction is thermodynamically favoured under standard-state conditions at $1000\ \mathrm K$

[2]

(c)

Using your answer to (a), calculate $\Delta_\mathrm r G^\circ$ at $1200\ \mathrm K$ State whether the forward reaction is thermodynamically favoured under standard-state conditions at this temperature.

[3]

Question 6

Paper 2Hard12 marks

Calcium oxide is produced by heating limestone, which contains calcium carbonate. The standard Gibbs energy change, $\Delta_\mathrm r G^\circ$ for the decomposition is shown in Figure 1. Assume that $\Delta_\mathrm r H^\circ$ and $\Delta_\mathrm r S^\circ$ remain constant over the temperature range shown.

(a)

Write a balanced equation, including state symbols, for the thermal decomposition of calcium carbonate.

[1]

(b)

Use Figure 1 to estimate $\Delta_\mathrm r G^\circ$ at $1000\ \mathrm K$

[1]

(c)

Use Figure 1 to determine $\Delta_\mathrm r H^\circ$ and $\Delta_\mathrm r S^\circ$ for the decomposition. Give signs and units, and show how you obtain both values.

[3]

(d)

Using your values from (c), determine the temperature at which $\Delta_\mathrm r G^\circ=0$ State at which temperatures the forward decomposition is spontaneous under standard-state conditions.

[2]

(e)

At $1000\ \mathrm K$ a gas stream keeps the carbon dioxide partial pressure in the kiln at $0.10\ \mathrm{bar}$ For the reaction as written, take

Q=\frac{p(\mathrm{CO_2})}{p^\circ},\qquad p^\circ=1.00\ \mathrm{bar},

with pure solids omitted from $Q$ Under these conditions,

\Delta_\mathrm r G=\Delta_\mathrm r G^\circ+RT\ln Q,

where $R=8.31\ \mathrm{J\,K^{-1}\,mol^{-1}}$

Determine the carbon dioxide partial pressure at which $\Delta_\mathrm r G=0$ at $1000\ \mathrm K$ Hence decide whether the forward decomposition is spontaneous at $p(\mathrm{CO_2})=0.10\ \mathrm{bar}$ and assess the claim that a positive $\Delta_\mathrm r G^\circ$ at $1000\ \mathrm K$ means that the decomposition cannot be spontaneous.

[5]

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