Collision Theory and activation energy

You're viewing free preview questions — 4 questions previewing here — subscribe to unlock 76 more, plus the Full Question Bank, Mock Papers & Worksheets.Upgrade

Collision Theory and activation energy — Free MYP4 Chemistry Practice Questions

1QuestionDefinition of activation energyConcept Practice

3 marks~5 minCriterion A

The reaction coordinate diagram below shows two curves for the same reaction: an uncatalyzed pathway (solid curve) with activation energy

120 \text{ kJ mol}^{-1}

and a catalyzed pathway (dashed curve) with activation energy

75 \text{ kJ mol}^{-1}

Define activation energy. [1]

Identify which pathway produces a faster reaction rate and justify your answer by comparing the two activation energy values. [1]

Using collision theory, explain how the lower activation energy of the catalyzed pathway results in a greater proportion of successful collisions at the same temperature. [1]

Solutions

2QuestionDefinition of activation energyAssessment Practice

4 marks~6 minCriterion D

Nitrogen monoxide (

\text{NO}

) forms in car engines when

\text{N}_2

and

\text{O}_2

react at temperatures above

1500\ °\text{C}

. This reaction has an activation energy of approximately

500\ \text{kJ mol}^{-1}

, far higher than most reactions occurring at Earth's surface. Once released,

\text{NO}

contributes to serious atmospheric problems. Catalytic converters are fitted to vehicles to promote the decomposition reaction

2\text{NO} \rightarrow \text{N}_2 + \text{O}_2

Explain why the reaction between

\text{N}_2

and

\text{O}_2

does not occur at Earth's surface temperatures. [1]

Explain how temperatures above

1500\ °\text{C}

inside a car engine allow this reaction to proceed. [1]

Analyse the health and environmental impacts of

\text{NO}

emissions, and evaluate the effectiveness of catalytic converters in reducing these impacts. [2]

Solutions

3QuestionEffect of activation energy on reaction rateAssessment Practice

5 marks~8 minCriterion B

A student investigates how activation energy affects the rate of decomposition of

\text{H}_2\text{O}_2\text{(aq)}

, using five different catalysts. Oxygen gas production is measured at constant temperature.

Reaction	A	B	C	D	E
Activation energy (kJ/mol)	40	55	70	50	85
Initial rate (mL/s)	8.2	3.5	1.1	2.0	0.4

Deduce the relationship between activation energy and initial rate of reaction. [1]

Explain this relationship using collision theory. [2]

Identify the anomalous data point and justify why it does not fit the expected trend, using collision theory in your answer. [2]

Solutions

4QuestionGraphical interpretation (energy distribution concept – qualitative)Assessment Practice

7 marks~11 minCriterion C

A student investigates the rate of reaction between substance X and hydrochloric acid at five temperatures. The results are:

Temperature (°C)	20	30	40	50	60
Initial rate (mol dm $^{-3}$ s $^{-1}$ )	0.002	0.005	0.012	0.028	0.065

Four Maxwell–Boltzmann energy distribution curves (A, B, C, D) for this reaction are shown in the diagram. Curve A has the highest, narrowest peak; curve D has the lowest, broadest peak; curves B and C are intermediate. A vertical line marks

E_a

on the energy axis.

Possible identities for substance X, with

E_a

for reaction with hydrochloric acid:

Substance	Zinc	Magnesium	Calcium	Iron
$E_a$ (kJ mol $^{-1}$ )	54	42	30	68

Deduce which curve corresponds to 20°C and which corresponds to 60°C. [2]

The rate increases from 0.002 to 0.065 mol dm

^{-3}

^{-1}

as temperature rises from 20°C to 60°C. Using collision theory, explain what the curves reveal about the fraction of molecules exceeding

E_a

at these two temperatures. [2]

Using the rate data and your answer to (b), evaluate which substance is most likely to be X. Justify your reasoning. [3]

Solutions

Questions 5-80

Unlock these questions with Premium

That's every free question here — 4 of 80.

+76 more questions, plus Mock Papers & Worksheets, are waiting in Premium.

Upgrade