Practice Questions - Week 8 - Thermodynamics Flashcards

1
Q

A reaction that is exergonic will be spontaneous. True or False?

A

True

Reactions that have a negative ∆G (∆G < 0) release free energy and are called exergonic reactions. Handy mnemonic: EXergonic means energy is EXiting the system.

A negative ∆G means that the reactants, or initial state, have more free energy than the products, or final state. Exergonic reactions are also called spontaneous reactions, because they can occur without the addition of energy.

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2
Q

An endergonic reaction requires an input of energy to proceed. True or False?

A

True

Reactions with a positive ∆G (∆G > 0) require an input of energy and are called endergonic reactions.

In this case, the products, or final state, have more free energy than the reactants, or initial state.

Endergonic reactions are non-spontaneous, meaning that energy must be added before they can proceed.

You can think of endergonic reactions as storing some of the added energy in the higher-energy products they form.

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3
Q

By definition, a spontaneous reaction is one in which

Energy is released

Energy is absorbed

The energy change is zero

The reaction is fast

The reaction is slow

A

Energy is released

(A spontaneous reaction is thermodynamically favourable, has a negative ∆G and release energy.

The energy released in the reaction is independent of its rate, ∆G does not provide information about the kinetics of the reaction.)

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4
Q

Reactions that are thermodynamically unfavourable (i.e energy consuming reactions) can occur in living cells because they can be coupled with reactions which have a negative ΔG. True or False?

A

True

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5
Q

Which statement about ΔG is incorrect?

A positive or negative ΔG tells us which direction the reaction will proceed

ΔG depends on the concentration of the reactants and products

ΔG is affected by temperature

ΔG is affected by pressure and pH

ΔG is negative for endergonic reactions

A

ΔG is negative for endergonic reactions

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6
Q

Which equation defines a system at equilibrium?

ΔG > 0

ΔG° = ΔG

ΔG = 0

ΔG = RT ln ([products]/[reactants])

A

ΔG = 0

When a reaction reaches equilibrium, the free Gibbs energy of the reactants is equal to the free Gibbs energy of the products and therefore, the variation of free Gibbs energy is zero, ΔG = 0.

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7
Q

Consider these reactions:

What is the ΔG°’ of the last reaction?

  • 44kJ/mol

-18 kJ/mol

+18 kJ/mol

+44 kJ/mol

A

-18 kJ/mol

(The ΔG°’ of combined reactions, is the sum of the individual ΔG°’.

Look at the direction of the second equation: it is the opposite direction to the combined reaction; therefore, the ∆G will have the opposite energy in the combined reaction.

When you add them together

∆G°’ = -31 + 13 = -18 kJ/mol)

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8
Q

If the ΔG’0 of the reaction A → B is –40 kJ/mol, under standard conditions the reaction ________________________ .

is at equilibrium.

will never reach equilibrium

will not occur spontaneously.

will proceed at a rapid rate.

will proceed spontaneously from left to right.

A

will proceed spontaneously from left to right.

(If the ΔG’0 of the reaction A → B is –40 kJ/mol, under standard conditions the reaction will proceed spontaneously from left to right)

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9
Q

The reaction A + B → C has a ΔG0’ of –20 kJ/mol at 25 °C.

Starting under standard conditions, one can predict that _____________________ .

at equilibrium, the concentration of B will exceed the concentration of A.

at equilibrium, the concentration of C will be less than the concentration of A.

at equilibrium, the concentration of C will be much greater than the concentration of A or B.

C will rapidly break down to A + B.

when A and B are mixed, the reaction will proceed rapidly toward formation of C.

A

at equilibrium, the concentration of C will be much greater than the concentration of A or B.

(The reaction A + B → C has a ΔG0’ of –20 kJ/mol at 25 °C.

Starting under standard conditions, one can predict that the reaction will proceed spontaneously from left to right, and at equilibrium, the concentration of C will be much greater than the concentration of A or B)

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10
Q

A chemical reaction is faster when

∆G > 0

∆G < 0

the activation energy is high

the activation energy is low

A

the activation energy is low

(The rate of a chemical reaction depends on the activation energy and is independent of the ∆G)

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11
Q

Oxidation refers to the

the loss of oxygen

the gain of oxygen

the loss of electrons

the gain of electrons

A

the loss of electrons

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12
Q

An oxidising agent

loses oxygen

gains oxygen

loses electrons

gains electrons

A

gains electrons

(An oxidising agent accepts electrons from a reducing agent. The oxidising agent becomes reduced)

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13
Q

Biological oxidation-reduction reactions always involve ________________ .

transfer of electron(s).

direct participation of oxygen.

mitochondria.

formation of water.

transfer of hydrogens.

A

transfer of electron(s).

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14
Q

In biological redox reactions, hydrogen ions are usually transferred along with electrons. True or False?

A

True

(For example, NADH and NADPH are universal reducing agents used in biological redox reactions and transfer 1 H+ and 2 electrons)

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15
Q

Standard reduction potential (E°) is measured in Volts in standard conditions, and relates with the affinity for electrons of an electron acceptor. True or False?

A

True

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16
Q

Which of the following is not true about enzymes:

They increase ∆G of reactions.

They are usually made of amino acids.

They lower the activation energy of chemical

reactions.

Each one is specific to the particular substrate(s) to

which it binds.

A

They increase ∆G of reactions.