RATE OF REACTIONCHAPTER 1

In this chapter, you will learn to:

Analyse the rate of reaction.Synthesise factors affecting the rate of reaction.

Synthesise ideas on the collison theoryLearn about practising scientific knowledge to enhance quality

of life.

1.1 ANALYSING RATE OF REACTION

LEARNING OUTCOMES

State what rate of reaction is.Identify observable changes to reactants or products for

determining rate of reaction.Determine average rate of reaction.

Determine the rate of reaction at any given time from a graph.Solve numerical problems involving average rate of reaction.Solve numerical problems involving rate of reaction at any

given time.

INTRODUCTIONThe rate of reaction refers to:

The speed at which the reactants are converted into products in a chemical reaction.

The observable change in quantity of a reactant with time.The observable change in quantity of a product with time.

Rate of reaction: Observable change in quantity of reactant/ product

Time taken for the change to occurThe quantity of reactants and products refers to:

Mass of solidsConcentration of liquidsVolume of gases

Continue…Example: Reaction between marble chips (calcium carbonate)

and dilute acid.CaCO3 (s) + 2HNO3 (aq) Ca(NO3)2 (aq) + H2O (l) + CO2 (g)

Reactants Products In this reaction, the observable change are:

A decrease in mass of the reactant, CaCO3 with time. The volume of carbon dioxide gas produce increase with time.

The rate of reaction inversely proportional with time.Explanation:

A reaction is fast, or its rate of reaction is high, if the time taken for the reaction to occur is short.

Likewise, a reaction is slow, or its rate of reaction is low if the time taken for the reaction to occur is long.

Fast ReactionsType of Reaction Example

Burning • Sodium burns rapidly in air to form sodium oxide. 4Na (s) 2Na2O (s)

Reaction between dilute acids and

carbonates

• Dilute acid react with carbonates to release carbon dioxide.

2HCl + CaCO3 (s) CaCl2 (aq) + H2O + CO2

Reaction between a reactive metal and

water or dilute acids

• Very reactive metals like potassium and sodium react vigorously with water to release hydrogen gas.

2K (s) + 2H2O (l) 2KOH (aq) + H2 (g)

• Mg, Zn and Al react with dilute acids to release hydrogen gas rapidly.

Mg (s) + 2HCl (aq) MgCl2 (aq) + H2 (g)

Precipitation of ionic compounds

When barium(II) chloride, BaCI2 and potassium chromate(vl), K2CrO4 solution are added together, a yellow precipitation of barium chromate (vI), BaCrO4 is formed immediately.

Slow ReactionsType of

ReactionExample

Precipitation of sulphur

• A slow reaction occurs when a dilute acid is added to sodium thiosulphate solution Na2S2O3. A yellow precipitation forms after several seconds.

Na2S2O3(aq) + 2HCl(aq) 2NaCl(aq) + S(s) + H2O(l) + SO2(g)

Photosynthesis • Carbon dioxide and water combine in the presence of chlorophyll and sunlight to form glucose and oxygen in green plants. This process occurs slowly.

Rusting • Iron rusts slowly in the presence of water and oxygen to form hydrated iron(II) oxide, Fe2O3.H2O or rust.