4) Reaction Rates and Equilibrium Flashcards
Define the rate of reaction.
The change in concentration of a reactant or a product in a given time.
What four factors affect the rate of a chemical reaction?
- Concentration.
- Temperature.
- Use of a catalyst.
- Surface area.
What is the effect of concentration on the rate of a reaction in terms of frequency of collisions?
- Increase in concentration increases the number of particles in the same volume.
- The particles are closer together and collide more frequently.
What is the effect of the pressure of gases on the rate of a reaction in terms of frequency of collisions?
- The concentration of gas molecules increases as the same number of gas molecules occupy a smaller volume.
- The gas molecules are closer together and collide more frequently, leading to more effective collisions.
What two conditions ensure an effective collision?
- Particles colliding with the correct orientation.
- Particles have sufficient energy to overcome the activation energy.
How is the reaction rate calculated from a graph measuring how a physical quantity changes with time?
Using gradients.
How could the progress of a reaction be followed?
- Monitoring the decrease in concentration of a reactant.
- Monitoring the increase in the concentration of a product.
What is a catalyst?
A substance that alters the rate of a reaction by providing an alternative route without being used up.
How does a catalyst increase the rate of a chemical reaction?
Provides an alternative reaction pathway with a lower activation energy.
Explain what is meant by a homogenous catalyst.
A homogenous catalyst has the same physical state as the reactants.
Explain what is meant by a heterogeneous catalyst.
A homogenous catalyst has a different physical state from the reactants.
Why do catalysts have great economic importance and benefits for increased sustainability?
- They lower temperatures.
- Therefore reducing energy demand from the combustion of fossil fuels with a resulting reduction in CO2 emissions.
What are two features of a Boltzmann distribution?
- No molecules have zero energy - the curve starts at the origin.
- The area under the curve is equal to the total number of molecules.
Use ‘Rates & Equilibrium’ to test knowledge of drawing a Boltzmann distribution.
Rate knowledge 1-5.
Use ‘Rates & Equilibrium’ to test knowledge of drawing the effect of temperature on a Boltzmann distribution.
Rate knowledge 1-5.
Use ‘Rates & Equilibrium’ to test knowledge of drawing the effect of a catalyst on a Boltzmann distribution.
Rate knowledge 1-5.
Explain how a higher temperature affects the rate of a chemical reaction.
- More molecules have energy greater than or equal to the activation energy.
- Therefore a greater proportion of collisions will lead to a reaction.
What does the symbol “⇌” indicate?
That the reversible reaction is in equilibrium.
What is meant by Dynamic Equilibrium?
A dynamic equilibrium exists in a closed system when:
- The rate of the forward reaction is equal to the rate of the reverse reaction.
- The concentrations of reactants and products do not change.
If the forward reaction is exothermic (ΔH is negative), how does an increase in temperature affect the position of equilibrium?
- The position of equilibrium is shifted to the left.
- More reactants are made.
If the forward reaction is exothermic (ΔH is negative), how does a decrease in temperature affect the position of equilibrium?
- The position of equilibrium is shifted to the right.
- More products are made.
If the forward reaction is endothermic (ΔH is positive), how does an increase in temperature affect the position of equilibrium?
- The position of equilibrium is shifted to the right.
- More products are made.
If the forward reaction is endothermic (ΔH is positive), how does a decrease in temperature affect the position of equilibrium?
- The position of equilibrium is shifted to the left.
- More reactants are made.
How does pressure affect the position of equilibrium?
Increasing the pressure of the system will shift the position of equilibrium to the side with fewer molecules, reducing the pressure of the system.
When discussing the changes in pressure in terms of the position of equilibrium, what must you always state?
Whether there are more moles on the left or right side of the equation.
Why does a catalyst not affect the position of equilibrium?
A catalyst increases the rate of both forward and reverse reactions in an equilibrium by the same amount.
Use ‘Rates & Equilibrium’ to test knowledge of generating an expression for Kc.
Rate knowledge 1-5.
What does a Kc value of 1 indicate?
A position of equilibrium that is halfway between reactants and products.
What does a Kc value > 1 indicate?
A position of equilibrium that is towards the products.
What does a Kc value < 1 indicate?
A position of equilibrium that is towards the reactants.
Explain why increasing the concentration of H2O2(aq) increases the rate of decomposition.
- More particles per unit volume.
- Therefore more collisions per second.
Explain how the catalyst can increase the rate of decomposition of H2O2(aq).
- The reaction takes an alternative route.
- Activation energy is lowered.
High pressures and low temperatures would give the maximum equilibrium yield of methanol. Explain why the actual conditions used in the chemical industry might be different from those above.
-Too expensive and dangerous to use high pressure.
Too slow to use a low temperature.
Suggest two ways in which the use of catalysts helps chemical companies to make their processes more sustainable.
- Catalyst not used up in reaction.
- Reactions take place at lower temperatures with lower energy demand and lower activation energy.
- Use less fuel so less carbon dioxide emitted into the atmosphere.
- Different reactions can be used with better atom economy.
Use collision theory to explain the changes in the rate of a reaction as it proceeds.
- As the reaction proceeds, the concentration decreases.
- The rate of collision decreases.
- The reaction stops when all of one reagent is used up.
Suggest and explain two reasons why catalysts are used in industrial processes.
- To save energy/money by allowing process to run at a lower temperature.
- Goes faster to save time.
