3.2.2 Reaction Rates Flashcards
What is the equation used to calculate rate?
Rate = change in concentration / time
What is the unit for rate of reaction?
mol dm⁻³ s⁻¹
What must particles do in order to react?
- Collide with sufficient energy (activation energy)
- Collide with the correct orientation
Do most collisions result in a reaction?
- No
What are the factors that affect rate of reaction?
- Temperature
- Pressure
- Concentration
- Surface area
- Catalyst
What is the effect of increasing temperature on rate of reaction and why?
- Increasing temperature increases the rate of reaction
- A higher proportion of particles have energy greater than the activation energy
- Many more successful collisions per second, so the rate increases
What is the effect of increasing concentration/pressure on rate of reaction and why?
- Increasing concentration/pressure increases the rate of reaction
- More particles in a given volume -> more frequent successful collisions
What are the variables in an experiment that can be monitored to calculate the rate of reaction?
- Concentration of reactant or product
- Gas volume of products
- Mass of substances formed
How to calculate rate from a concentration-time graph?
- Draw a tangent
- Work out the gradient of the tangent using the equation: Gradient = change in y / change in x
What is a catalyst?
- A substance that increases the rate of reaction but is not used up in the reaction
How do catalysts work and how do they increase the rate of reaction?
- Catalysts provide an alternative reaction pathway (with a lower activation energy)
- With a lower activation energy, more particles have sufficient energy, leading to more frequent successful collisions and an increased reaction rate
What does homogeneous catalyst mean?
- A catalyst that is in the same phase as the reactants
- Eg. a liquid catalyst mixed with liquid reactants
What does heterogeneous catalyst mean?
- A catalyst that is in a different phase to the reactants
- Eg. gaseous reactants passed over a solid catalyst
What are catalytic converters?
- Devices in vehicles to reduce toxic emissions and prevent photochemical smog
Define activation energy.
- The minimum energy that particles must collide with for a reaction to occur
Name some important features of Boltzmann distribution.
- Area under the curve = total number of molecules
- Area under the curve does not change when conditions alter
- The curve starts at the origin
- Curve does not touch or cross the energy axis
- Only molecules with energy greater than activation energy can react
What are the axes on a Boltzmann distribution?
- X-axis: Energy
- Y-axis: Number of molecules with a given energy
Draw a labelled Boltzmann Curve with labels of average energy, activation energy, and most probable energy. Draw in a different colour the effect of increasing temperature.
- T1 < T2 (T2 represents higher temperature)
- Curve shifts towards the right at higher temperature
- Higher proportion of molecules exceed activation energy
- Reaction rate increases
Draw a labelled Boltzmann Curve showing the effect of a catalyst on rate of reaction.
- A catalyst lowers activation energy (Ec < Ea)
- More molecules exceed the activation energy with a catalyst, increasing reaction rate
