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MCAT-GENERAL CHEMISTRY > Thermodynamics > Flashcards

Thermodynamics Flashcards

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1
Q

the laws of thermodynamics underlie any even in which ______ is transformed

A

energy

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2
Q

the Zeroth Law

A

if two systems are both in thermal equilibrium with a third system, then the two initial systems are in thermal equilibrium with one another

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3
Q

if systems are in thermal equilibrium, what does this imply about their temperatures?

A

their temperatures must be the same

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4
Q

the First Law

A

the total energy of the universe is constant, energy may be transformed from one form to another, but it cannot be created or destroyed

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5
Q

an isolated system has a constant ______

A

amount of matter and ENERGY: no transformation of the energy is possible

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6
Q

how can a system increase its overall energy?

A

if work is put into its system

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7
Q

what happens when energy flows into a system from the surroundings?

A

the energy of the system increases (+) and the energy of the surroundings decrease

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8
Q

what happens when energy flows out of a system into the surroundings?

A

the energy of the system decreases (-) and the energy of the surroundings increase

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9
Q

enthalpy, H

A

the measure of the heat energy that is released or absorbed when bonds are broken and formed during a reaction that’s run at constant pressure

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10
Q

when a bond is formed, energy is:

A

released, enthalpy change is negative

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11
Q

when a bond is broken, energy is:

A

put into the bond, enthalpy change is positive

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12
Q

heat of reaction

A

enthalpy change, delta H

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13
Q

when is enthalpy change negative, exergonic?

A

when the products of a chemical reaction have stronger bonds than the reactants, so that more energy is released in the making of product bonds than was put in to break chemical bonds

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14
Q

how do you calculate enthalpy change?

A

enthalpy of products - enthalpy of reactants

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15
Q

exothermic

A

energy is released overall from the system, enthalpy change is negative

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16
Q

endothermic

A

energy is absorbed into the system, enthalpy change is positive

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17
Q

standard conditions

A

298K (25 degrees Celsius), pressure is 1 atm, all solids and liquids are assumed to be pure, solutions are at a concentration of 1 M

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18
Q

standard heat of formation

A

the amount of energy required to make one mole of a compound from its constituent elements in their natural or standard state

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19
Q

what does it mean if standard heat of formation is a positive value?

A

an input of heat is required to make the compound from its constituent elements

20
Q

what does it mean if standard heat of formation is a negative value?

A

making the compound from its elements gives off energy

21
Q

Hess’s law

A

if a reaction occurs in several steps, then the sum of the energies absorbed or given off in all the steps will be the same as that for the overall reaction

22
Q

what does it mean that enthalpy is a state function?

A

the enthalpy change is independent of the pathway of reaction

23
Q

what happens to the value of enthalpy change if reaction is reversed?

A

the sign of enthalpy change is reversed too

24
Q

what happens to the value of enthalpy change if an equation is multiplied by a coefficient?

A

the enthalpy change must be multiplied by that same value

25
Q

enthalpies can be viewed as the energy stored in the chemical bonds of a compound that denotes how much energy is required to:

A

break the bond homolytically

26
Q

how do you calculate the enthalpy change of reaction?

A

sum of BDE of bonds broken - sum of BDE of bonds formed

27
Q

second law of thermodynamics

A

the disorder of the universe increases in a spontaneous process

28
Q

entropy

A

disorder or randomness, S

29
Q

what is the sign of entropy change if randomness increases and order decreases in a reaction?

A

positive

30
Q

what is the sign of entropy change if randomness decreases and order increases in a reaction?

A

negative

31
Q

what is the value of enthalpy change in a reverse reaction?

A

the same magnitude as that of the forward reaction but with opposite signs

32
Q

can reactions in which entropy decreases occur?

A

yes, but it would require either an input in energy or else it must gain energy from making more stable bonds

33
Q

The Third Law

A

absolute zero is a state of zero-entropy

34
Q

Gibbs free energy (delta G)

A

the energy that’s available (free) to do work from a chemical reaction

35
Q

what is the spontaneity of a reaction determined by?

A

changes in enthalpy and in entropy, included by G

36
Q

what is the formula for Gibbs free energy

A

G=H-TS

37
Q

what does it mean if Gibbs free energy is negative?

A

it is spontaneous in the forward direction

38
Q

what does it mean if Gibbs free energy is zero

A

the reaction is at equilibrium

39
Q

what does it mean if Gibbs free energy is positive

A

it is nonspontaneous in the forward direction

40
Q

if delta G is positive for a reaction, then what is the value of delta G for the reverse reaction?

A

it would be the same magnitude but opposite sign, so that the reverse reaction is spontaneous

41
Q

what does entropy depend on?

A

temperature; increased temperature=entropy has greater significance

42
Q

the universe tends towards…

A

increasing disorder (positive S) and stable bonds (negative H), a favourable condition of S and H will result in spontaneous processes

43
Q

what is the delta G of the overall reaction?

A

the difference between the energy of the products and the energy of the reactants

44
Q

the activation energy determines:

A

the kinetics of the reaction: it is the extra energy the reactants are required to overcome

45
Q

thermodynamics predicts:

A

the spontaneity and the equilibrium of reaction, not the rates (kinetics)

46
Q

microscopic reversibility

A

the reverse reaction has the same magnitude for all thermodynamic values but of the opposite sign, and the same reaction pathway but in reverse (mirror images)

47
Q

what is different for forward and reverse reactions?

A

activation energy

MCAT-GENERAL CHEMISTRY (6 decks)

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