Thermodynamics

Question 1

What is a chemical system?

Answer 1

All reactants and products are the immediate surrounding environment.

Question 2

what is a closed system?

Answer 2

the system exchanges energy, but does not matter with the environment outside the system.

Question 3

open system;

Answer 3

the system exchanges energy and matter with the environment outside the system.

Question 4

what does the universe represent?

Answer 4

• the system and the environment outside the system.

Question 5

What is the first law of thermodynamics?

Answer 5

• in any chemical change the total amount of energy in the universe remains constant, although the form of the energy may change.
  examples;
• kinetic; heat, motion and pressure,
• potential energy; bonds and gradients.
• biological systems depend on energy transformation.

Question 6

What does the internal energy of a system include?

Answer 6

• The internal energy of a system includes; the potential energy of bonds and kinetic energy (heat and pressure).

Question 7

what is enthalpy?

Answer 7

• the energy content of the bonds within the system.
• very difficult to measure directly and not useful.
• we tend to measure this when reactants turn into products. we can measure this by measuring the change of heat in the system.

Question 8

What is an exothermic reaction?

Answer 8

• (-) enthalpy. - change in H
• tends to be a spontaneous reaction that releases heat.

Question 9

what is an endothermic reaction?

Answer 9

• an endothermic reaction absorbs heat.
• positive enthalpy (often is not spontaneous but depends).

Question 10

what is an isothermic reaction?

Answer 10

• a reaction that neither absorbs nor releases heat.

Question 11

what is the second law of thermodynamics?

Answer 11

• systems move spontaneously from order to disorder, and the total entropy of the system is continually increasing.

Question 12

what is entropy?

Answer 12

• defines how spread out or dispersed energy is in the system.
• an increase in entropy means that the energy in that system is more dispersed.

Question 13

give an example of entropy.

Answer 13

• a hot pan cooling.
• the molecules in the pan that were moving rapidly represent concentrated energy.
• the pan does cool down but its energy was dispersed widely around its atmosphere around it.
• the pan did not cool down by concentrating its heat elsewhere.
• energy disperses or spreads out unless it is hindered from doing so.

Question 14

For example; why isn’t gasoline exploding all of the time?
- this reaction is highly exothermic- when gas combusts to form water and CO2, the total chemical bonds go from a higher to lower energy state.

Answer 14

• this reaction is highly exothermic- when gas combusts to form water and CO2, the total chemical bonds go from a higher to lower energy state.
• the entropy of the system increases- the gaseous water and CO2 are more random or dispersed than the reactants (gasoline and oxygen).

Question 15

what reactions tend to be more spontaneous?

Answer 15

• reactions that release heat and reactions that increase entropy (+S).

Question 16

what is Gibbs Free Energy?

Answer 16

• measures the energy difference between products and reactants and takes into account both enthalpy and entropy.
• change in G= changeH-T(change inS)

Question 17

what is an exergonic reaction?

Answer 17

• a negative change in Gibbs free energy = spontaneous.
• on with a negative change in Gibbs free energy and a positive change in E

Question 18

what is an endergonic reaction?

Answer 18

• this is a positive change in Gibbs free energy = non-spontaneous reaction.

Question 19

what happens if GFE = 0?

Answer 19

• The reaction is at equilibrium, with no net transfer of heat or energy.

Question 20

what is GFE dependent on?

Answer 20

• it is dependent on temperature, pH and relative concentrations of products or reactants.
• temperature; 298 K.
• pH; 7.
• 1 M of reactant and product.

Question 21

would the following be spontaneous?
A (-) ΔHrxn and a (+) ΔSsystem

Answer 21

• exothermic (release heat) and exergonic more randomness (entropy).
• always spontaneous.

Question 22

would the following be spontaneous?
A (+) ΔHrxn and a (+) ΔSsystem

Answer 22

• endothermic ( absorb heat= non-spon) + more disorder (spon) = sometimes spontaneous.

Question 23

would the following be spontaneous?
A (-) ΔHrxn and a (-) ΔSsystem

Answer 23

• exothermic (spontaneous) + less disorder (non- spon)
• sometimes is spontaneous.

Question 24

would the following be spontaneous?
A (+) ΔHrxn and a (-) ΔSsystem

Answer 24

• endothermic (non-spon) + less disorder more order (non-spon) = never spontaneous.

Question 25

how does Gibbs free energy change as reactants are increased compared to the products?

Answer 25

- as we increase reactants compared to products the Gibbs free energy becomes more exergonic. - release more energy.

Question 26

what happens as products increase release relative to the reactants?

Answer 26

- Gibbs free energy becomes more endergonic, we require more energy to get the reaction going. There are fewer reactants so more selectivity is needed when transferring them to products requiring the input of energy.

Question 27

How are non-standard conditions Gibbs free energy used as a biological strategy?

Answer 27

- even reactions with fairly large +G can develop into exergonic reactions if the [reactants] is substantially greater than the [products]. - you will see this as a common strategy to drive some of the endergonic reactions of glycolysis forward.

Question 28

How is it possible that a reaction with (+) Gibbs free energy occurs in our bodies all the time?

Answer 28

- they are coupled with a reaction that is highly exergonic resulting in a net negative Gibbs free energy. - this is the whole rationale behind why the body phosphorylates and dephosphorylates it as a source of energy for the body. - this high energy phosphodiester bond when broken has a negative change in Gibbs free energy, this can be coupled with another reaction with a positive change in Gibbs free energy.

Question 29

How do enzymes help us out?

Answer 29

- they help to reduce the activation energy, the activation energy is the energy required to break chemical bonds that lead to the formation of new ones.

Question 30

what is redox potential?

Answer 30

- also known as reduction potential. - represented by E and defines the affinity of a molecule for an electron. - A molecule with a more positive E is a better electron acceptor, and a molecule with a smaller or more negative E is a better electron donor.

Question 31

Example: Fe+3 + e-  Fe+2 Eo’ = 0.77 V Cu+2 + e-  Cu+ Eo’ = 0.16 V Based on the above information, is it energetically more favourable for iron to donate its electrons to copper, or copper to iron?

Answer 31

- copper has the lower E suggesting that it is more energetically favourable for the copper to donate and the iron to accept.

Question 32

why do we care about redox reactions?

Answer 32

- redox reactions are crucial to the function of a wide variety of reactions within the cell. particularly the electron transport chain. - the ETC consists of electron carriers arranged in order from low energy affinity to high energy affinity, when an electron is transferred from a molecule of low electron affinity to higher electron affinity we get a release of energy. - this energy can be harnessed to make an H+ gradient need to make ATP in mitochondria.