CBI4 - Biomolecular Reactions

Question 1

What is thermodynamics.

Answer 1

Study of relative energies of reactants and products and exchanges of energies.

Question 2

Define a system, surroundings and boundary.

Answer 2

System is set of biochemical reactions within a boundary. Surroundings is the surrounding area around the system (includes the entire universe).
Boundary is line between system and surroundings.

Question 3

Discuss a closed system.

Answer 3

Transfer of energy between system and surroundings.

Question 4

Discuss an open system.

Answer 4

Transfer of energy and mass between system and surroundings.

Question 5

Discuss an isolated system.

Answer 5

No transfer of energy or mass between system and surroundings.

Question 6

What is the first law of thermodynamics.

Answer 6

Conservation of energy - energy cannot be created or destroyed only transferred between different types.

Question 7

How is the total energy of a system and surroundings altered.

Answer 7

Not altered. Total energy is not affected.

Question 8

Define temperature with units.

Answer 8

Measure of average kinetic energy of an object. Kelvin, K.

Question 9

Define heat with units.

Answer 9

Transfer of energy from one object to another. kJmol-1

Question 10

What is enthalpy.

Answer 10

Amount of energy stored in a chemical bind at a constant pressure.

Question 11

Discuss what factors affect bond enthalpy.

Answer 11

Type of atom, bond length and environment.

Question 12

How do you calculate enthalpy change of a reaction.

Answer 12

Total enthalpy of products minus total enthalpy of reactants.

Question 13

Define an exothermic reaction.

Answer 13

Reaction where enthalpy change is negative. Reactants have more energy than products.

Question 14

Define an endothermic reaction.

Answer 14

Enthalpy change of reaction is positive. Products have more energy than reactants.

Question 15

Define Hess’ law.

Answer 15

Enthalpy change of a reaction is independent of the route taken.

Question 16

Define difference between transition state and activated complex.

Answer 16

Transition state is species at energy maxima. Activated complex defines the configurations near the transition state.

Question 17

Define entropy.

Answer 17

Measure of total microstates possible within a system as a result of the energies.

Question 18

What is the 2nd law of thremodynamics.

Answer 18

Entropy of the entire universe will always increase over time.

Question 19

How do you calculate the entropy change of a reaction.

Answer 19

Entropy of product minus entropy of reactants.

Question 20

Discuss a reaction where entropy change is negative.

Answer 20

Reaction decreases the dispersal of energy.

Question 21

Define two formulas for Gibbs energy.

Answer 21

Change in Gibbs energy is change in enthalpy minus temperature multiplied by change in entropy.
Change in Gibbs energy is negative gas constant multiplied by temperature multiplied by ln of equilibrium constant.

Question 22

What indicates a spontaneous reaction.

Answer 22

Negative change in Gibbs energy.

Question 23

Define activation energy.

Answer 23

Energy required to reach energy maxima - transition state.

Question 24

What defines the rate determining step.

Answer 24

Step with highest energy transition state.

Question 25

Difference between kinetics and thermodynamics.

Answer 25

Kinetics defines rate at which a reaction proceeds. Thermodynamics defines if a reaction proceeds.

Question 26

How do catalysts lower activation energy.

Answer 26

Provide alternative pathway with lower activation energy.

Question 27

Name three attacking species.

Answer 27

Nucleotides. Electrophiles. Free radicals.

Question 28

Define difference between nucleophile and electrophile.

Answer 28

Nucleophile is electron donor. Electrophile is electron acceptor.

Question 29

Name 4 types of common reactions.

Answer 29

Addition. Elimination. Substitution. Rearrangement.

Question 30

Name two types of nucleophilic substitution mechanisms.

Answer 30

SN1 and SN2.

Question 31

Define difference between SN1 and SN2 reaction.

Answer 31

SN1 is unimolecular rate determining step. Formation of carbonation initially, by leaving group leaving. SN2 reaction is bimolecular rate determining step. Nucleophile attacks as leaving group leaves.

Question 32

Define redox reactions.

Answer 32

Reduction is gain of electrons. Oxidation is loss of electrons.

Question 33

Which halide is mostly nucleophilic in polar protic solvents and why.

Answer 33

Iodide. Least hindered by hydrogen bonding and it is least electronegative.

Question 34

Which halide is most nucleophilic in polar aprotic solvent.

Answer 34

Fluoride. Smallest solvent shell around halide. Greatest nucleophilic strength.

Question 35

How to calculate enthalpy change of a reaction.

Answer 35

Average bond enthalpy of bonds in reactants summed together. Average bond enthalpy of bonds in products summed together. Reactants minus products.

Question 36

How does enthalpy change affect reaction pathway.

Answer 36

Does not affect.

Question 37

How to calculate total entropy change.

Answer 37

Entropy change of system added to entropy change of surroundings.

Question 38

Do ordered or disordered systems have higher entropy.

Answer 38

Disordered systems have higher entropy.

Question 39

Define a micro state.

Answer 39

The way in which energy is distributed.

Question 40

How do enzymes work as catalysts.

Answer 40

Active site of enzyme stabilises the transition state in the reaction pathway lowering its energy and so lowers the activation energy.