Unit 2) 1) Equilibria , Factors Affecting Equilibrium And The Equilibrium Constant Flashcards

1
Q

What does it mean by “ a reaction is in equilibrium”

A

Some reactions never go to completion but are in a state of dynamic equilibrium
A chemical reaction is said to be in equilibrium when the rate of the forward reaction is equal to the rate of the reverse reaction : so the forward reaction and E verse reaction do not stop

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2
Q

At equilibrium the concentration of reactants and products will be ________ but not ________

A

At equilibrium the concentration of reactants and products will be constant but not equal

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3
Q

What is a closed system

In a closed system heat is able to be ________ to or from surroundings

A

For an equilibrium to establish the reaction must take place in a closed system : this is where the chemicals are trapped and nothing is added or removed , but heat is allowed to be transferred to or from the surroundings

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4
Q

What did Henri le chatelier say about equilibrium

A

“If a system is at equilibrium and a change is made in any of the conditions ,then the system responds to counteract the change as much as possible”

  • in other words if you make a change to a reaction at equilibrium , the system will alter the concentrations to minimise the effect until equilibrium is re established.
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5
Q

How can the position of equilibrium be altered

A
  • altering concentration of reactant or product
  • altering pressure (increasing or decreasing )
  • altering temperature (increasing or decreasing )
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6
Q

Effect of concentration on equilibrium position

A

Increasing concentration of reactant - equilibrium shifts right
Increasing equilibrium of product - equilibrium shifts left

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7
Q

Effect of temperature on equilibrium position

A

Increasing temperature - equilibrium shifts in direction of the endothermic reaction
Decreasing temperature- equilibrium shifts in direction of the exothermic reaction

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8
Q

Effect of pressure on equilibrium position

A

Increase in pressure - equilibrium shifts to side with least moles of gas
Decrease in pressure - equilibrium shifts to side with most moles of gas

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9
Q

Composition of equilibrium mixtures

A

Look at notes for examples and explanation

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10
Q

What is equilibrium constant

A

The equilibrium constant is a mathematical relationship that shows how the concentration of the products vary with the concentration of the reactants

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11
Q

What symbol does the equilibrium constant have , what symbol does it have when in terms of concentration

A

Equilibrium constant is - K

In terms of constant Kc

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12
Q

Equilibrium constant of general equation aA + bB —— > < cC + dD

A

Kc = [C]^c x [D]^d / [A]^a x [B]^b
- where the brackets indicate the concentration of species present at equilibrium , this is then raised to the power of the number of moles of that species from the balanced equation

(Look in notes it makes more sense)

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13
Q

What is a homogenous equilibrium

A

In a homogenous equilibrium , all the species present at equilibrium are all in the same state

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14
Q

Worked out examples of equilibrium constant expressions

A

Look in notes ! Important

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15
Q

Does K have units

A

No , K does not have units

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16
Q

What happens when a pure solid / pure liquid is present at equilibrium
Example

A

When a pure solid / liquid is present at equilibrium it’s concentration takes a value of 1
This is NOT true for aqueous solutions
Example in notes

17
Q

What is a heterogenous equilibria

- example

A
  • in a heterogenous equilibria , not all the species present are in the same state
  • an example of a heterogenous equilibrium is heating calcium carbonate in a closed system so that the carbon dioxide gas produced cannot escape and equilibrium is established : look in notes for details
18
Q

What can affect the position of equilibrium , but not the equilibrium constant

A

Changing the concentration or pressure may affect the position of equilibrium, but it does not affect th equilibrium constant ,K.

19
Q

What happens to equilibrium when concentration or pressure is changed (in terms of constant )

A

When the concentration (or pressure in a chemical equilibrium involving gases) is changed , the position of equilibrium also changes - until the ratio of products and reactants return to original value (position of equilibrium changes until numerical value of K is de established )

20
Q

What effect does a catalyst have on position of equilibrium and value of K

A
  • presence of a catalyst has no effect on the position of equilibrium
  • therefore a catalyst has no effect on the numerical value of the equilibrium constant K
21
Q

Effect of temperature on equilibrium constant K

A

The value of equilibrium constant , K , is dependent on temperature

22
Q

Increase in temperature effect on K

  • in endothermic reactions
  • in exothermic reactions
A
  • in an endothermic reaction , increase in temp favours products , so ratio of products / reactants increases so K increases
  • in endothermic reactions increase in temp causes increase in yield of products so value of K increases
  • in an exothermic reaction , an increase in temp favours the reactants so ratio of products /reactants decreases and therefore K decreases.
  • in exothermic reactions an increase in temp causes a decrease in the yield of the product and the value of K decreases
23
Q

What does the equilibrium constant value give indication of

A

Since the equilibrium constant is the ratio of concentration of products divided by the concentration of reactants, it’s actual value gives guidance to the extent of a reaction once it has reached equilibrium

24
Q

The greater the value of Kc the ________ the concentration of products compared to reactant

A

Greater

- in other words the further the reaction has gone to completion

25
Q

Value of Kc an extent of reaction

A

Much less than 1 (or 10-3 ) - position of equilibrium is to the left (effectively no reaction )
Approximately 1- neither side is favoured , significant quantities of reactants and products at equilibrium
Much greater than 1 - to the right , reaction is effectively complete