rate of reactions
TRANSCRIPT
Rate of Reactions
Fast or Slow Reactions
• Extremely slow reactions– Iron rusting– Limestone weathering
• Extremely fast reactions– Explosion
Measuring Rate of Reactions
• Some rate of reactions have detectable change with respect to time
• Changes that are observable like– When a volume of gas is given off– When this is a change in mass during the
reaction– When there are temperature changes– When there are colour changes– When a precipitate forms– When there are pH changes
Collision Theory
• For a reaction to occur– The reacting particles must collide into
each other– The reacting particles must possess
enough activation energy
• Once products are formed, effective collisions have occurred
Factors affecting Rate of Reactions
• Temperature of the substances used (reactants)
• Concentration of the substances used (reactants)
• Pressure on the reaction
• Particle size (surface area) of the substances used (reactants)
• Presence of catalyst
Temperature
• Rate of reaction increases with increasing temperature
• High temperature, particles have greater heat energy
• Particles move faster with greater kinetic energy
• Leading to more collisions between particles
• Increased probability of effective collision• Reactions take place faster
• Speed of reaction doubles when the temperature
rises by 10 C
TemperatureAmt of product formed
Time
Higher temperature
Lower temperature
Concentration
• Rate of reaction increases with increasing concentration
• Higher concentration, more reacting particles are present
• Greater probability of an effective collision
• Faster rate of reaction
Concentration – Same no. of molesAmt of product formed
Time/s
Higher concentration
Lower concentration
Concentration – Different no. of molesAmt of product formed
Time/s
Higher concentration
Lower concentration
Pressure
• Rate of reaction increases with increasing pressure
• Higher pressures, reacting particles are closer together
• Increasing concentration per unit volume
• Greater probability of an effective collision
• Faster rate of reaction
PressureAmt of product formed
Time/s
Higher pressure
Lower pressure
Particle Size
• Rate of reaction increases when particle size decreases
• Smaller particles has greater surface area than larger particles of the same mass
• Greater surface area for collision by another reacting particle
• Greater probability of an effective collision• Faster rate of reaction
Particle sizeAmt of product formed
Time/s
Smaller particle size
Larger particle size
Catalyst
• Presence of catalyst increases rate of reaction
• (Presence of inhibitors decreases rate of reaction)
• Catalysts lower activation energy of reactants
• Aids the formation of unstable intermediate products
• Increases probability of formation of products
• Faster rate of reaction
CatalystAmt of product formed
Time/s
Use of catalyst
Absence of catalyst
CatalystEnergy
Time/s
Use of catalyst
Absence of catalyst
Ea
Ea
Catalyst
Definition: A substance which increases the rate of a chemical reaction by providing an alternative pathway with a lower activation energy but remains unchanged at the end of the reaction