Thermodynamics II

Question 1

Give an example of a spontanous exothermic reaction

Answer 1

Dissolving 1 mole of CuSO4 in 250cm3 water will give a temperature rise of 70°C

Question 2

Are all spontaneous reactions endothermic

Answer 2

No

e.g. ice melts at room temperature

Question 3

Give an example of a spontaneous endothermic reaction

Answer 3

NH4NO3 -> NH4(+)(aq) + NO3(-)(aq) where delta H= +28.05kJmol-1

Question 4

Are ice crystals ordered or disordered in arrangment

Answer 4

Ice crystals are highly ordered

Question 5

Are liquid water molecules ordered or disordered in arrangement

Answer 5

Liquid water is fairly ordered

Question 6

Are water vapour molecules ordered or disordered in arrangment

Answer 6

Water vapour and steam are random in arrangement and so disordered

Question 7

What is the second law of thermodynamics

Answer 7

During spontaneous change, energy and matter become more disordered

Question 8

In the second law of thermodynamics what does energy refer to

Answer 8

The release of enthalpy (exothermic reaction)

Question 9

In the second law of thermodynamics what does matter refer to

Answer 9

An increase in entropy

Question 10

What does the fact that not all spontaneous reactions are endothermic mean

Answer 10

That energy and matter are not equally important and one dominates in a spontaneous reaction

Question 11

What is the Gibbs Free Energy equation

Answer 11

ΔG = ΔH - TΔS

Question 12

What does ΔH refer to in the Gibbs free energy equation

Answer 12

Enthaply change

Question 13

What does ΔS refer to in the Gibbs free energy equation

Answer 13

Entropy change

Question 14

What does T refer to in the Gibbs free energy equation and what unit does this value possess

Answer 14

Temperature in K (+273 to °C)

Question 15

What does it mean if ΔG

Answer 15

The reaction is spontaneous if ΔG is a negative value

Question 16

What does it mean if ΔG > 0

Answer 16

The reaction is not spontaneous if ΔG is a positive value

Question 17

According to Gibbs free energy how can a reaction still be spontaneous if ΔH is positive (endothermic)

Answer 17

If a reaction is endothermic the reaction can still be spontaneous if the ΔS value is large enough that a negative ΔG value is still produced

Question 18

What value is ΔG is a reversible reaction once the reaction has reached equlibrium

Answer 18

ΔG = 0 and the reaction seems to stop

Question 19

In regards to reversible reactions what reactions occur at equlibirum

Answer 19

There is a mixture of the forwards and backwards reactions which are occurring at a constant rate resulting in a mixture of the products of the two reactions being present and the reaction appears to have stopped

Question 20

What is the equation of a reversible reaction at equilibrium

Answer 20

aA + bB cC + dD

Question 21

Once a reversible reaction is at equilibrium what equation can you use to find the equilibrium constant

Answer 21

K= (C^c x D^d/ A^a x B^b)equilibrium

Question 22

If K is a big value what does this mean

Answer 22

The concentration of products is higher and the concentration of reactants is lower

Question 23

If K is a small value what does this mean

Answer 23

The concentration of products is lower and the concentration of reactants is higher

Question 24

Why do you have to wait until a reaction has reached equilibrium until you calculate the equilibrium constant

Answer 24

The composition of the substance no longer changes once the reaction has reached equilibrium