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Speed of ReactionKey Concepts:

1. Speed of a reaction can be measured by :(i) change in mass of reactant or product over time(ii) volume of gas liberated over time(iii) temperature / pressure changes(iv) colour / precipitate or pH change

2. Speed of a reaction can be followed through by analyzing a reaction rate curve.

3. Collision Theory:For a reaction to occur,

the reacting particles must collide with one another;

the particles must possess sufficient activation energyAny factor that increases the rate of effective collision will increase the speed of reaction.

4. The main factors which can affect the speed of a chemical reaction are:

temperature particle size

concentration pressure catalyst (To be discussed in WS 2)

5. Temperature of reactants: The higher the temperature, the faster the speed of reaction because:

1. At a higher temperature, reacting particles have more energy. Theymove faster and collide more frequently.

2. Due to the increase in the energy of reacting particles, there are morereacting particleshaving the activation energy required for the reactionto occur.

This leads to an increase in the number of effective collisions per unit time.

For every 10oC rise in temperature, the speed of reaction approximately doubles.

6. Particle size ( surface area ) of reactants: A decrease in the size of the particles of the reactants (larger surface area)

Volume

ofgas(cm3)

Time Taken (minutes)

Plateau indicates the end of reaction determined by limiting reagent

Gradient of slope indicates the rate of reaction determined by temperature, particle size orconcentration, pressure and catalyst.

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increases the speed of reaction because:

The area of contact between the reacting particles increases, the number ofeffective collisions per unit time also increases.

7. Concentration of reactant: An increase in concentration of the reactants increases the speed of reaction

because:

When the concentration of a reactant is increased, there are more reactingparticles per unit volume.

The frequency of collisions between the reacting particles thus increases.

This leads to an increase in the number of effective collisions per unittime.

8. Pressure of reactant (for gases only): An increase in pressure of the reactants increases the speed of the reaction

because:

When the pressure of a gas is increased, there are more gas particles perunit volume.

The frequency of collisions between the gas particles thus increases.

This leads to an increase in the number of effective collisions per unittime.

Key Concepts:

1. A catalyst is a substance that changes the speed of the reaction but it remains chemicallyunchanged at the end of the reaction.

2. Catalysts provide an alternative pathway for reactions to occur. In the catalyzed pathway,less energy is required for the reaction to occur, so the activation energy is lowered.

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3. Catalysts only changes the speed of reaction, they do not increase the yield of products.

4. Some common industrial uses of catalysts:

Catalysts Uses

iron Manufacture of ammoniavanadium(v) oxide Manufacture of sulphuric acidNickel Manufacture of margarineEnzymes in yeast Manufacture of ethanol