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MCAT General Chemistry > Thermochemistry > Flashcards

Thermochemistry Flashcards

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1
Q

The law of conservation of energy

A

Energy can neither be created nor destroyed, but that all thermal, chemical, potential, and kinetic energies are interconvertible

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2
Q

Isolated Systems

A

no exchange of energy/matter with the environments (bomb calorimeters)

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3
Q

Closed Systems

A

can exchange energy but not matter with the environment

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4
Q

Open Systems

A

can exchange both energy and matter with the environment

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5
Q

Isothermal

A

temperature remains constant

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6
Q

Adiabatic

A

no heat exchange occurs

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7
Q

Isobaric

A

pressure of a system remains constant

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8
Q

Isovolumetric

A

aka isochoric

volume remains constant

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9
Q

Heat

A

the transfer of thermal energy from one object to another

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10
Q

Endothermic

A

Reactions that absorb thermal energy

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11
Q

Exothermic

A

Reactions that release thermal energy

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12
Q

Constant Volume and Constant Pressure Calorimetry

A

Used to indicate conditions under which the heat flow is measured

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13
Q

Equation to calculate heat absorbed or released

A

q=mcΔT

m= mass
c= specific heat
ΔT= change in temperature
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14
Q

State Functions

A

described by the macroscopic properties of the system, and the magnitudes of these properties depend on only the initial and final states of the system, not the path.
Include: pressure, density temperature, volume, enthalpy, internal energy, free energy, and entropy

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15
Q

Enthalpy

A

(H) used to express the heat changes at constant pressure

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16
Q

Standard heat of formation

A

the enthalpy change that would occur if one mole of a compound was formed directly from its elements in their standard states

17
Q

Standard heat of reaction

A

the hypothetical enthalpy change that would occur if one mole of a compound was formed directly from its elements

18
Q

Hess’s Law

A

states that enthalpies of reactions are additive

the reverse of any reaction has an enthalpy of the same magnitude as that of the forward reaction (sign is opposite)

19
Q

Bond Dissociation Energy

A

an average of the energy required to beak a particular type of bond in one mole of gaseous molecules

20
Q

Bond Enthalpy

A

the standard heat of reaction can be calculated using the values of bond dissociation energies of particular bonds

21
Q

Entropy

A

(S) the measure of the distribution of energy throughout a system

22
Q

Gibbs free energy

A

combines the two factors that affect the spontaneity of a reaction: changes in enthalpy (ΔH) and changes in entropy (ΔS)

ΔG= ΔH - TΔS

23
Q

If ΔG is negative

A

the reaction is spontaneous

24
Q

If ΔG is positive

A

the reaction is nonspontaneous

25
Q

If ΔG is zero

A

the reaction is in equilibrium (ΔH=TΔS)

26
Q

If ΔH is negative and ΔS is positive

A

reaction is spontaneous at all temperatures

27
Q

If ΔH is positive and ΔS is negative

A

reaction is nonspontaneous at all temperatures

28
Q

If ΔH is positive and ΔS is positive

A

spontaneous at very high temperatures

29
Q

If ΔH is negative and ΔS is negative

A

spontaneous at very low temperatures

30
Q

Reaction Quotient

A

(Q) once a reaction has started the standard state conditions no longer hold so we use Q to determine where we are in the reaction (before eqlbm, after eqlbm or at eqlbm)

31
Q

Standard Conditions

A

298K
1 atm
1 M

32
Q

Standard Temperature and Pressure

A

273K
1 atm

** used for ideal gas problems

33
Q

Specific Heat

A

the specific heat required to raise the temperature of 1 gram of substance by 1 degree

34
Q

Heat Absorbed or Released in a Process (Equation)

A

q=mcΔt
m- mass
c- specific heat
t- temp

35
Q

During Phase Changes we use

A

q=mL

L- latent heat

36
Q

Entropy Equation

A

ΔS = Qrev/T

37
Q

Equation for Gibbs Free Energy

A

ΔG= ΔH - TΔS

38
Q

Standard Free Energy for the Reaction Equation

A

ΔGrxn = -RT lnKeq

MCAT General Chemistry (11 decks)

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