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

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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 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 3

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]

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