Hydrocarbons

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Hydrocarbons — Free MYP5 Chemistry Practice Questions

1QuestionSaturated vs unsaturated hydrocarbonsConcept Practice

4 marks~6 minCriterion A

When ethene (C2H4) reacts with bromine water, the time for complete decolourisation was recorded at three temperatures.

Temperature (°C)	20	30	40
Time (s)	120	60	30

Use the relationship

\text{rate} = \dfrac{1}{\text{time}}

throughout.

Calculate the reaction rate at 20°C. [1]

Calculate the reaction rates at 30°C and 40°C. Present all three rates in the format:

Temperature (°C)	20	30	40
Reaction rate (s $^{-1}$ )	___	___	___ [1]

The time halves with each 10°C rise. Explain, using collision theory, why increasing temperature increases the reaction rate of ethene with bromine water. [2]

Solutions

2QuestionAlkenes Reactivity compared to alkanesAssessment Practice

4 marks~6 minCriterion C

The graph below shows the time taken for bromine water to decolorize when added to five different alkenes (A–E) and one alkane (F) under the same conditions.

Interpret the graph and answer the following questions.

Describe the overall trend shown in the graph regarding the reactivity of alkenes compared to the alkane.

Identify which alkene data point is an anomaly and explain why it is considered an anomaly.

State a conclusion about the role of the carbon-carbon double bond in the reactivity of alkenes, referencing the graph data.

Suggest one reason why the anomalous alkene might react more slowly than expected.

Solutions

3QuestionUses of hydrocarbons (fuels, plastics)Assessment Practice

4 marks~6 minCriterion B

The table below shows the standard enthalpy of combustion (

\Delta H_c

) for six consecutive alkanes.

Alkane	methane	ethane	propane	butane	pentane	hexane
Number of carbon atoms ( $n$ )	1	2	3	4	5	6
$\Delta H_c$ (kJ mol $^{-1}$ )	−890	−1560	−2220	−2877	−3536	−4194

Construct a graph of

\Delta H_c

(kJ mol

^{-1}

) against

n

. Describe the relationship shown. [2]

Deduce the average increase in

\Delta H_c

per additional

CH_2

group. Use this value to predict

\Delta H_c

for heptane (

C_7H_{16}

). Show your working. [1]

Justify why

\Delta H_c

becomes more negative as chain length increases, with reference to the bonds broken and bonds formed during combustion. [1]

Solutions

4QuestionAlkenes Double bonds / General formula (CₙH₂ₙ)Assessment Practice

6 marks~9 minCriterion D

A fruit-ripening facility uses ethene (

\text{C}_2\text{H}_4

) gas to accelerate banana ripening. The room measures

10\ \text{m} \times 8\ \text{m} \times 3\ \text{m}

. In a controlled process,

0.50\ \text{kg}

of ethene is released. Assume ideal gas behaviour, room temperature

25\ ^\circ\text{C}

, and atmospheric pressure

1.00 \times 10^5\ \text{Pa}

.

Molar mass of ethene:

28.0\ \text{g mol}^{-1}

;

R = 8.31\ \text{J mol}^{-1}\text{K}^{-1}

; room volume:

240\ \text{m}^3

Calculate the volume of ethene released under these conditions. [2]

Show that the ethene occupies less than 1% of the room volume, and explain what this suggests about oxygen availability for workers. [2]

Evaluate the reliability of the ideal gas law for predicting safe ethene concentration levels in this facility. [2]

Solutions

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