CIE A Level Chemistry: Rate of Reaction and Collision Theory (Chapter 8.1)

Rate of Reaction

Speed of a chemical reaction, measured in mol dm⁻³ s⁻¹.

Rate Calculation

Rate = change in amount (mol dm⁻³) / time (s).

Moles Calculation

Moles = mass (g) / molar mass (g mol⁻¹).

Concentration Change

Concentration = amount (mol) / volume (dm³).

Activation Energy (Eₐ)

Minimum energy for a successful collision.

Effective Collision

Correct orientation and sufficient energy for reaction.

Ineffective Collision

Incorrect orientation or insufficient energy; no reaction.

Collision Frequency

Number of collisions per unit time.

Catalyst

Substance increasing reaction rate without being consumed.

Alternative Pathway

Lower activation energy route provided by a catalyst.

Concentration Effect

Higher concentration increases collision frequency.

Pressure Effect

Increased pressure raises collision frequency in gases.

Volume Conversion

400 cm³ = 0.400 dm³.

Time Conversion

1.0 minute = 60.0 seconds.

Rate Example

Rate = 2.08 x 10⁻⁵ mol dm⁻³ s⁻¹.

Collision Theory

Particles must collide correctly to react.

Sufficient Energy

Energy required for effective collisions.

Chemical Reaction

Process resulting from effective collisions.

Orientation

Arrangement of particles during collision.

Reaction Mixture

Combined substances undergoing a chemical reaction.

Molar Mass

Mass of one mole of a substance in g.

Concentration-time graph

A graph that shows how the concentration of reactants and products changes over time during a reaction.

Isomerisation of cyclopropane

The process where cyclopropane is transformed into propene.

Reactant

A substance that undergoes change during a chemical reaction.

Product

A substance that is formed as a result of a chemical reaction.

Rate of reaction formula

Rate of reaction = change in the amount of reactants or products (mol dm−3) / time (s).

Average rate of reaction

The rate calculated over a specified time interval.

Initial rate of reaction

The rate of reaction at the very beginning, often determined by drawing a tangent at the start of the concentration-time curve.

Concentration of cyclopropane at 0 mins

1.50 mol dm−3.

Concentration of propene at 0 mins

0.00 mol dm−3.

Rate of reaction from 0 to 5 mins

0.0009 mol dm−3 s−1.

Rate of reaction from 15 to 20 mins

0.0005 mol dm−3 s−1.

Rate-concentration graph

A graph that shows how the rate of reaction changes with varying concentrations of reactants or products.

Directly proportional relationship

A relationship where doubling one quantity results in doubling the other quantity.

Concentration of cyclopropane at 0.5 mol dm−3

Rate of reaction is 0.33 × 10−3 mol dm−3 s−1.

Concentration of cyclopropane at 1.0 mol dm−3

Rate of reaction is 0.67 × 10−3 mol dm−3 s−1.

Concentration of cyclopropane at 1.5 mol dm−3

Rate of reaction is 1.0 × 10−3 mol dm−3 s−1.

Temperature effect on reaction rate

A change in temperature will change the rate of reaction.

Tangent method

A technique used to find the rate of reaction at a specific point on a curve by drawing a tangent.

Short time intervals

Using brief periods to calculate the rate of reaction for increased accuracy.

Concentration of propene at 30 mins

1.05 mol dm−3.

Concentration of propene at 35 mins

1.13 mol dm−3.

Concentration of propene at 40 mins

1.17 mol dm−3.