Section 2: Equilibrium Flashcards Preview

Chemistry OCR 2017 Paper 1 > Section 2: Equilibrium > Flashcards

Flashcards in Section 2: Equilibrium Deck (25)
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What is a dynamic equilibrium?

The forward and reverse reactions are going at the same rate and there's no overall change in the concentrations of the reactants and products.


In what system can a dynamic equilibrium occur?

Closed system (a system where nothing can get in or out) at a constant temperature.


In which systems can equilibria be set up?

Physical system - changes physical stage
Chemical system - when the moles of the reactants change until equilibrium is reached


What is the equilibrium constant equation?

Kc = [D]d [E]e / [A]a [B]b


What is a homogenous reaction?

All products and reactants are in the same stages, e.g. Gases


What is a heterogenous equation?

Reactants and products are in different states


What is the rules for calculating kc for heterogeneous equations?

If the mixture is heterogeneous only gases and aqueous substances go into the expression for the equilibrium constant (any solids or liquids get left out)


What is partial pressure?

In a mixture, each individual has exerts its own pressure


How do you calculate total pressure?

By adding all the partial pressures up


How to calculate partial pressure of a gas in a mixture?

Mole fraction of gas x total pressure of the mixture


How to calculate mole fraction of a gas in a mixture?

Number of moles of gas / total number of moles of gas in the mixture


When is the GAS equilibrium Kp used?

Reversible reaction where some or all of the reactants and products are gases


What is the equation for Kp?

Kp = p(D)d p(E)e / p(A)a p(B)b


How to use Kp for heterogeneous equilibria?

Don't include solids or liquids into the expression


What is Le Chatelier's Principle?

If there's a change in concentration, pressure or temperature, the equilibrium will move to help counteract the change


What happens if the position of the equilibrium moves to the left?

You'll get more reactants


What happens if the position of the equilibrium moves to the right?

You'll get more products


What affects the value of Kc?



What happens to the equilibrium if you increase the temperature?

The equilibrium shifts in the endothermic direction (positive H) to absorb the heat.


What happens to the equilibrium is you decrease the temperature?

The equilibrium shifts in the exothermic direction (negative H) direction to try to replace the heat.


How does more product formed affect Kc?

Increases KC


How does less product formed affect Kc?

Will decrease


How does concentration affect Kc?

It doesn't. Thus the reaction needs to change the concentrations in order to keep Kc the same


How is the value of Kp affected by change in pressure?

Increasing pressure shifts the equilibrium to the side with fewer gas molecules to reduce pressure

Decreasing pressure shifts the equilibrium to the side with more gas molecules. This raises the pressure again.


How do catalysts affect the rate of Kp/Kc ?

They have no effect. This is because a catalyst will increase the rate of both the forward and backward reactions by the same amount.