Equilibrium

Question 1

What is an irreversible reaction?

Answer 1

Most chemical reactions carry on occurring until all of the reactants have turned into products or until one or both of the reactants has run out. Therefore we can say that the reaction has gone to completion and only occurs in one direction (reactants - products). An example of this would be an acid-base titration

Question 2

What’s a reversible reaction?

Answer 2

Irreversible reactions do not always occur when reactants are combined together. In many reactions not only will reactants combine to form products, but products will recombine to form the reactants. Both forward and back reactions occur. Such reactions are said to be reversible.

Question 3

Define a reversible reaction

Answer 3

In a reversible reaction the rate of the forward reaction is equal to the rate of the back reaction

Question 4

What does a full arrow head demonstrate?

Answer 4

A complete reaction in one direction

Question 5

Are reactants or products on the right?

Answer 5

Reactants are on the left
Products are on the right

Question 6

What is a forward reaction?

Answer 6

Where reactant molecules are reacting together and forming product molecules

Reactant —> product

Question 7

What is a reverse reaction?

Answer 7

Where product molecules are reacting together and forming reactant molecules

Products —> reactants

Question 8

When can dynamic equilibrium occur?

Answer 8

When two reactants are reacting together to form products

Question 9

What is dynamic equilibrium? Description not definition

Answer 9

This is when the rates of the forward and reverse reactions are equal so that as fast as the reactants are being used up, the products are converted back into reactants again.

This means that there is no further observational change in the concentration of reactants and the concentration of products at equilibrium

An equilibrium only applies as long as the system remains closed. In an isolated system, no materials are being added or taken away and no external conditions are being altered

Question 10

How do you know you have reached dynamic equilibrium?

Answer 10

When the two rates are equal there is no further change in the concentration of the reactants or products, although both reactions continue, and the system is said to have attained dynamic equilibrium

Question 11

What is the definition of dynamic equilibrium?

Answer 11

The rate of forward reaction is equal to the rate of the reverse reaction

Question 12

What is the position of equilibrium (POE)?

Answer 12

The proportions of products to reactants in an equilibrium mixture

Question 13

What is Le Chatelier’s Principle?

Answer 13

If a system in equilibrium is subjected to a change which disturbs the equilibrium, the system responds in such a way as to counteract the effect of the change

Question 14

Le Chatelier’s Principle concentration rule

Answer 14

An increase in concentration of a substance in equilibrium tends to push the equilibrium to the opposite side in order to restore the balance

Question 15

Le Chatelier’s Principle pressure rule

Answer 15

An increase in pressure on a system in equilibrium always favours the side with fewer number of molecules

Question 16

Le Chatelier’s Principle temperature rule

Answer 16

An increase in temperature always favours the endothermic direction.
Why? The system can counteract the increase in temperature (the input of heat energy) by favouring the reaction that absorbs heat energy; the endothermic process, the temp will then decrease

A decrease in temperature always favours the exothermic direction. Because the temp will then increase to counteract the inmbalance

Question 17

Negative (delta)H = ?
Positive (delta)H = ?

Answer 17

Negative is exothermic
Positive is endothermic

Question 18

What would a catalyst affect? The position of equilibrium (how it shifts)? The rate at which you achieve equilibrium?

Answer 18

No affect on the position, as they work in a way that affects both the forward and back reaction equally. They speed up the rate of which equilibrium is achieved but not the composition of the equilibrium mixture.

Question 19

You are asked to state what you would observe when an equilibrium is affected by a change in conditions, what would you state?

Answer 19

You are expected to use the information given and state any colour changes that would occur

Question 20

State and explain how the position of equilibrium changes when temperature/pressure/concentration changes

Question 21

State and explain how the yield of product/ reactant changes when temperature/pressure/concentration changes

Question 22

State and explain what is observed in the equilibrium reaction when the temperature/pressure/concentration changes

Question 23

A condition changes, the removal of product. How does this affect the POE?

Answer 23

POE will shift to form more product so counteracting the effect of the change

Question 24

All systems in dynamic equilibrium share the same three characteristics, what are they?

Answer 24

They all occur in a closed system

The rate of forward reaction is the same as the rate of the back reaction, so that the concentration of the reactants and products remain constant

The equilibrium can be attained from either direction beginning with only materials on one side of the choice. Hence such systems are described as reversible

Question 25

Define acids and bases

Answer 25

Acid is a proton donor
Bases are proton acceptors

Question 26

Define the pH scale

Answer 26

A level definition
or
Measure of the relative acidity or alkalinity of a solution

Question 27

Define Standard solution

Answer 27

Solution of known concentration made up using a volumetric flask