Chapter 4: Energy

Question 1

What are the three laws of thermodynamics?

Answer 1

1. total amount of energy in the universe is constant. Energy can neither be created nor destroyed but can be transformed 2. disorder of the universe always increases..aka all chemical and physical processes occur spontaneously only when disorder of the universe increases. 3. as the temperature of a perfect crystalline solid approaches zero…disorder approaches zero.

Question 2

What is an open system?

Answer 2

• matter and energy are exchanged between between the system and the surroundings

Question 3

What is a closed system?

Answer 3

• only energy is exchanged between the system and the surroundings

Question 4

State functions are independent of what?

Answer 4

• the path they take to get to their final products - they only depend on their initial and final states

Question 5

What are the three state functions?

Answer 5

• enthalpy, entropy and free energy L> heat and work are not.

Question 6

When energy is exchanged between system and surroundings it is exchanged as what?

Answer 6

• work/heat

Question 7

For the first law of thermodynamics what is the formula? (enthalpy) Also make note of exothermic and endothermic

Answer 7

• Delta H reaction= Hproducts - Hreactants
• Delta H = - = exothermic
• Delta H= + = endothermic

L> since enthalpy is a state function it is independent of the pathway and can be calculated for any reaction thus:

Delta H reaction = ΣdeltaH products - ΣdeltaH reactants

(remember stoichiometry)

Question 8

What denotes entropy, enthalpy and free enrgy?

Answer 8

S, H, G

Question 9

Spontaneous reactions are ______ aka energy is released

Answer 9

• exergonic

Question 10

Systems can be spontaneously get more ordered (decrease entropy aka s) IF the surroundings become more ____ and the overal disorder of the universe ___.

Answer 10

more disordered (increase entropy) , entropy increases

Question 11

Formula for entropy? (S)

Answer 11

• delta S uni= delta S sys + delta S surr

L> delta S uni= -….process does not occur but the reverse proess takes place spontaneously

L> =+, process is spontaneous

L> = 0…neither process occurs(organism dies)

Question 12

Equation for gibbs free energy?

Answer 12

Delta G= delta H- TDeltaS

L> Exergonic = spontaneous, releases energy

L> endergonic= nonspontaneous, requires energy

Question 13

What does the sign of Delta G tell us?

Answer 13

1. • = spontaneous which is favourable…exergonic
2. • =nonspontaneous which not favourable…..endergonic
3. 0= equilibrium..no change

Question 14

Delta G depends on what three things? Solution to these three?

Answer 14

• temp, pressure, concentration

L> reference point is needed….The standard free energy offers this…defines delta G at standard conditions… 25C…1 atm… 1 M reactan concentration….since all biochemical reactions occur in dilute aqueous mixtures…..Delta G knot prime+ Delta G at pH=7

Question 15

What is the formula for the standard free energy?

Answer 15

delta G knot= -RTlnKeq

L> Keq= Products at eq/ reactants at eq…..Keq= [C]^c[D]^d/[A]^a[B]^b

* if H concentration does not effect a chem rxn Delta G=Delta G knot prime

Question 16

Coupled reactions??

Answer 16

• allow the cell to harness energy produced by catabolism!

L> a non spontaneous reaction (+DeltaG) can be driven forward by coupling it with a spontaneous reaction (-DeltaG)…to produce a negative Delta G over all/

Question 17

How do nonspontaneous reactions move forward assuming constant temp?

Answer 17

• couple it with a spontaneous rxn that will supply enough energy to give an overall negative delta G OR
• change the relative concentratios of reactant and product so that the actual delta G will be neg

Question 18

what does the hydrophobic effect explain?

Answer 18

• why non polar molecules aggregate in water…why micelles and bilayers form….these processes result in decrese of entropy….the overall entropy includng the surrouding water ,molecules is higher…
• water forms solvent cages around solutes = decrease in entropy since water movement is restricted… delta g , delta h= positive and -Tdelta S is very positive….
• it is proportional to the surface area of contact between nonpolar molecules and water….aggregation of nonpolar molecules reduces surface area of their ontact with water and water becomes less ordered(entropy change is now positive aka S)
• TdeltS becomes negative….free energy of the process is negative and therefore is spontaneous…..this exlcusion of water by hydrophobic molecules plays a role in protein folding and assembly of supramolecular structures such as membranes

Question 19

ATP is produced how?

Answer 19

– using energy released by breaking down nutrients (catabolism) and by light reactions of photosynthesis. Hydrolysis of ATP releases 30.5kJ/mole of energy used to drive endergonic reactions.

Question 20

What types of endergonic processes does the hydrolysis of ATP drive? (3)

Answer 20

biosynthesis (anabolic), active transport, mechanical work

Question 21

Why is ATP hydrolysis so exergonic?

Answer 21

• products are more stable than the reactants because the final products:
  1. have less electrostatic repulsion ( of neg charges)
  2. have more resonance structures than reactions
  3. are more easily solvated than the reactants

Question 22

Phosphoryl group transfer potential??

Answer 22

the tendency of a phosphoryl-containing molecule to hydrolyze, resulting in its phosphoryl group being released as HPO4 (2-) or trasnferred to another molecule

Question 23

Phosphoryl group transfer potential:

• The greater the phosphoryl group transfer potential, the more ???

Answer 23

energy is released when a phosphoryl group is hydrolyzed ( and the more stable a molecule would be without its phosphoryl group)

Question 24

What makes ATP the energy currency?

Answer 24

• 1. it possesses an intermediate phosphoryl group transfer potential so it can be an intermediate carrier of phophoryl groups of high and low energy compounds. This makes it energy currence because cells tend to transfer phosphate by coupling reactions to ATP hydrolysis. 2. At Typical intracellular pH values the triphosphate unit of ATP carriers three or four negative charges which repel one another generating more energy…..3. The products of ATP hydrolysis are resonance hybrids making them much more stable in conserving energy. 4. The products ( ADP Pi or AMP and PPi) are more easily solvated than ATP resulting in ercreased repulsion bryerrn phosphoryl groups driving the hydrolytic reaction. 5. When atp is converted into ADP and Pi they are randomly oving increasing disorder and therefore increasing energy.

Question 25

Thermodynamics tells us ___ whereas kinetics tells us___.

Answer 25

• if a reaction is spontaneous or not…if it is than there will be more products than reactants at eq…aka reaction proceeds forward until it reaches eq….they release energy (exergonic)
• how fast the reaction will go

Question 26

Glucose reacts with oxygen to form carbon dioxide in water. Thermodynamics tells us that this reaction is spontaneous and very exothermic but kinetics tells us?

Answer 26

• that the rate at room temp is very slow….that is why glucose in contact with air doesnt simply burst into flames.

L> it will spontaneously combust but it will not suddenly combust unless enouh energy is applied to overcome the activation energy and or the activtion energy is lessened via enzymes.

Question 27

ex prob: Pyruvate oxidizes to form carbon dioxide and water liberating energy at a rate of 1142.2kJ/mol. If electron transport also occurs, ~12.5ATP molecules are produced. The free energy of hydrolysis of ATP is -30.5kJ/mol. What is the efficiency of ATP production?

(#ATP x 30.5kJ/mol divided by energy released(1142.2kJ/mol)) x 100

= (12.5x30.5/1142.2)100

=33.37%