Rate of Reaction is the change in concentration in unit time of any one reactant or product
Average Rate – Change in Concentration
Time taken
Instantaneous Rate of Reaction is the rate at a particular point in time during the reaction
To calculate the instantaneous rate of reaction
- Draw a tangent to the curve
- The tangent is the hypotenuse to a right angled triangle
- θ = angle by tangent to the horizontal axis
- Slope = tan θ = 18.5/1.2 = 15.4 cm³/min
On graphs:
- The reaction time is inversely proportional to concentration (x axis = time) i.e. the shorter the time, the greater the concentration
- When using the reciprocal (1/time) the reaction time is directly proportional to concentration i.e. the greater the time, the greater the concentration
Factors Affecting Reaction Rate
1. Temperature
- Increase in temperature – increase in reaction rate
- In some cases, an increase of 10 K can up to double reaction rate
2. Concentration
- Increase in concentration – increase in reaction rate
3. Particle Size
- Smaller particles – increase in reaction rate
- Finely divided solids – Greater surface area for reaction to occur over
Dust Explosions
The factors for a dust explosion to occur are:
- Finely divided combustible particles
- An enclosed space
- Enough oxygen to sustain combustion
- A spark to ignite combustion
4. Nature of Reactants
- Covalent bonds – slow reaction
- Bonds must be broken before reaction can occur – Rate will depend on bonds (Single bonds easier to break than double bonds)
- Ionic bonds – Quick in aqueous solution
- Ions pulled apart by water – instant reaction
5. Presence of Catalysts
- Can speed up or slow down reaction
- Catalyts work by lowering the energy required for a reaction to occur
