AP Chemistry 7.2 Direction of Reversible Reactions Study Notes - New Syllabus Effective fall 2024
AP Chemistry 7.2 Direction of Reversible Reactions Study Notes- New syllabus
AP Chemistry 7.2 Direction of Reversible Reactions Study Notes – AP Chemistry – per latest AP Chemistry Syllabus.
LEARNING OBJECTIVE
Explain the relationship between the direction in which a reversible reaction proceeds and the relative rates of the forward and reverse reactions.
Key Concepts:
- Reversible Reactions
7.2.A.1 Equilibrium and the Balance of Forward and Reverse Reaction Rates:
1. Rate of Reaction:
i. Forward Reaction Rate:
– The forward reaction rate is fast at the start as there are many reactants present.
– With the consumption of reactants, the rate decreases with the passage of time.
ii. Reverse Reaction Rate:
– The initial reverse reaction rate is zero as there are no products available.
– As products accumulate, the rate of the reverse reaction rises with time.
iii. At Equilibrium:
– The rates of the forward and reverse reactions are equal.
– There is no net change in reactant and product concentrations, although both reactions continue to take place.
2. Establishing Equilibrium:
Equilibrium is established when the rates of the forward and reverse reactions become equal. At this point:
1. Forward Reaction Rate: The rate at which reactants are converted into products.
2. Reverse Reaction Rate: The rate at which products are converted back into reactants.
Once these rates are equal, the concentrations of reactants and products remain constant over time, even though both reactions are still occurring. This is the state of dynamic equilibrium.
In essence, equilibrium is reached when the forward and reverse reactions are balanced, and no net change occurs in the system.
3. Le Chatelier’s Principle:
Le Chatelier’s Principle is that when equilibrium is perturbed by a change in concentration, temperature, or pressure in a system at equilibrium, the system shifts in a manner to reverse the change to achieve equilibrium.
i. Change in Concentration:
– Adding Reactant: Reverses equilibrium towards forward reaction, promoting production of products.
– Adding Product: Reverses equilibrium towards reverse reaction, promoting formation of reactants.
ii. Pressure Change (for Gaseous Reactions):
– Increased Pressure: Equilibrium is moved towards the side with fewer moles of gas.
– Reduced Pressure: Equilibrium is moved towards the side with more moles of gas.
iii. Temperature Change:
– Rising Temperature: Equilibrium is moved towards the endothermic side (gets hot).
– Lowered Temperature: Equilibrium is moved towards the exothermic side (gets cold).