Static and Dynamic Equilibrium

Question 1

Define reversible reaction, give two examples.

Answer 1

Products of reversible reactions can easily be converted back into the reactants.

Cobalt chloride (blue) + Water Hydrated cobalt chloride (pink)

Iron (III) nitrate (pale yellow) + potassium thiocyanate iron (III) thiocyanate (brown)

Question 2

Define irreversible reaction , give two examples.

Answer 2

Products cannot be converted back into reactants.

Combustion reactions of magnesium metal and steel wool in oxygen. Exothermic reaction.

Question 3

Define equilibrium.

Answer 3

A situation in which the concentration of reactants and species in a reaction remain constant over time.

Question 4

What are the two types of equilibrium?

Answer 4

Static and Dynamic

Question 5

What are the characteristics of static equilibrium?

Answer 5

• no further reactions occur between reactants and products
• rates of the forward and reverse reaction = 0
• reaction proceeds in one direction until one reactant is used up -> reaction stops

Question 6

What are the characteristics of dynamic equilibrium?

Answer 6

• forward and reverse reactions occur simultaneously and at the same rate
• reactants are converted into products and the products react to reform the reactants
• no net change in the concentrations of the reactants and products
• note that the concentrations of the reactants does not need to equal the products at this point

Question 7

Distinguish between open and closed system.

Answer 7

Open = matter and energy exchanged
Closed = only energy exchanged

Question 8

Define enthalpy.

Answer 8

Total energy in a system.
If delta H is greater than 0 = endothermic reaction.
If delta H is less than 0 = exothermic reaction

Question 9

Define entropy.

Answer 9

The randomness of a system. Reactions will favour movement towards a greater degree of randomness when delta S is greater than 0.

Question 10

Gibbs free energy takes into account both entropy and enthalpy to determine whether the reaction will occur at a given temp. What is the formula for this?

Answer 10

delta G = delta H - (T x delta S)

Question 11

Is combustion reversible or irreversible, and is it an endothermic or exothermic reaction?

Answer 11

Irreversible, exothermic

Question 12

What is the chemical formula for photosynthesis?

Answer 12

6H2O + 6CO2 -> (light) C6H12O6 + 6O2

Question 13

Is photosynthesis reversible or irreversible?

Answer 13

Irreversible.

Question 14

Is the enthalpy of reaction for photosynthesis positive or negative? What about entropy?

Answer 14

Enthalpy of reaction is positive, and therefore endothermic. Entropy change is negative as the system becomes more ordered.

It is therefore NOT spontaneous and can only occur when significant light energy is supplied and catalysts are present.

Question 15

What is the rate of reaction?

Answer 15

Change in concentration of products or reactants over time.

Question 16

The collision theory states that for a reaction to occur, the reactant particles MUST:

Answer 16

• physically collide with one another
• collide with enough energy to break bonds
• collide with the right orientation to allow bond formation

Question 17

What factors affect the rate of a reaction?

Answer 17

• temperature (higher temperature faster rate)
• concentration and pressure of the particles (higher pressure due to smaller volume can increase rate of reaction)
• particle size (more surface area faster rate)