PH1125 - Thermodynamics

Question 1

what do all living things require?

Answer 1

• a continuous supply of energy

Question 2

what is the relationship between wavelength and energy?

Answer 2

• the shorter the wavelength the higher the energy and vice versa

Question 3

what does photosynthesis provide to a plant? (2)

Answer 3

• provides chemical energy (ATP)

- stores captured energy as sugars

Question 4

what do thermodynamics tell us? (3)

Answer 4

• whether a reaction will occur or not
• tell use that a protein will fold
• predict the molecular shape of a drug
• why molecules cross biological membranes

Question 5

what is the first law of thermodynamics? (5)

Answer 5

• ENERGY CANNOT BE CREATED OR DESTROYED IT IS ONLY INTERCONVERTED
• there are lot of different types of energy
• energy can be changed from one form to another
• during the transformation, energy is neither created nor destroyed
• we can infer the total energy in the universe is constant

Question 6

what is the equation for the first law of thermodynamics? (4)

Answer 6

• ΔU = Ufinal - Uinitial = q + w
• U is energy
• q is heat absorbed by the system
• w is work done on the system

Question 7

where is q derived from in the first law of thermodynamics equation ?

Answer 7

• random molecular movement / vibration

Question 8

what is the formula for w?

Answer 8

• force x distance

Question 9

what is an exothermic process in term of q?

Answer 9

• releases heat where q is -ve

Question 10

what are the units for energy? (3)

Answer 10

• J (joules)
• kg m2 s-2
• N m

Question 11

what is the equation for enthalpy? (5)

Answer 11

• H = U + PV
• H is enthalpy
• U is energy
• P is pressure
• V is volume

Question 12

what is the second law of thermodynamics? (2)

Answer 12

• the universe is always moving towards maximum disorder

- or in nature the only processes that occur are those for which the entropy remains the same or increases

Question 13

what is the equation for the second law of thermodynamics? (4)

Answer 13

• S = kB ln W
• S is entropy
• kB is boltzmann constant
• W is the number of ways of arranging a system

Question 14

in the second law of thermodynamics what happens when temperature rises?

Answer 14

• the structure of any substance becomes more disordered

Question 15

what is the third law of thermodynamics?

Answer 15

• at absolute zero (0 K) the entropy of a perfect crystalline substance is 0

Question 16

what is the equation for gibbs free energy? (5)

Answer 16

• G = H - TS
• G is free energy
• H is enthalpy
• T is the temperature (in K)
• S is the entropy

Question 17

what is the gibbs free energy equation at a constant temperature and pressure?

Answer 17

• ΔG = ΔH - TΔS

Question 18

what is the difference between enthalpy and entropy?

Answer 18

• entropy is a measure of disorder in a system

- enthalpy is a measure of the overall amount of energy in the system

Question 19

what does a large ΔS mean in gibbs free energy equation?

Answer 19

• a reaction is more likely to happen

Question 20

what is the equation for free energy differences?

Answer 20

• ΔG = ∑ΔGf(products) - ∑ΔGf(reactants)

Question 21

what is the relevance of free energy to pharmacy? (3)

Answer 21

• enzymes are biological catalysts that accelerate most biochemical processes
• enzymes can be thought of as a mechanism for a system to achieve thermodynamic equilibrium
• an enzyme cannot promote a reaction that has a positive ΔG

Question 22

what happens in ΔG = ΔH - TΔS when ΔG is positive?

Answer 22

• the reaction is non-spontaneous and will not proceed in the forward direction unless coupled with an energetically favourable reaction

Question 23

What happens when ∆H is -ve and ∆S is +ve? (2)

Answer 23

• the reaction is exothermic and endotropically favoured

- t is spontaneous at all temperatures

Question 24

What happens when ∆H is -ve and ∆S is -ve? (2)

Answer 24

• the reaction is exothermic but endotropically disfavoured

- only spontaneous at low temperatures

Question 25

What happens when ∆H is +ve and ∆S is +ve? (2)

Answer 25

• the reaction is endothermic and entropically favoured

- only spontaneous at high temperatures

Question 26

What happens when ∆H is +ve and ∆S is -ve? (2)

Answer 26

• the reaction is endothermic but endotropically disfavoured

- it is not spontaneous at any temperature