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Geol 386 > 386 Thermodynamics > Flashcards

386 Thermodynamics Flashcards

1
Q

Definition of Thermodynamics

A

study of inter-conversion of heat and other forms of energy

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2
Q

definition of spontaneous reaction

A

physical or chemical change that occurs by itself

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3
Q

definition of non-spontaneous reaction

A

phyisical or change that does NOT occur by itself

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4
Q

Type of Thermodynamic Systems

A

Open
Closed
Isolated

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5
Q

What is an open thermodynamic system

A

system that can exchange both mass and energy with the surroundings

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6
Q

what is a closed system

A

system that can exchange heat but not mass with the surroundings

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7
Q

What is an isolated system?

A

a system where there is no exchange or either mass or heat with the surroundings

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8
Q

What’s the goal of the Laws of Thermodynamics?

A

Predict the behavious of physical and chemical systems

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9
Q

The First Law of Thermodynamics is also known as what?

A

Law of Conservation of Energy

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10
Q

What is the First Law of Conservation of Energy?

A

The total energy of the universe is constant.

Energy can neither be created nor destroyed

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11
Q

What is the Heat of Reaction?

A

quantity of heat required to return a system to its original temperation, after completion of the chemical reaction. There is a gain or loss of heat to do so.

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12
Q

What is an exothermic reaction?

A

chemical reqction where heat is released from the system

quantity of heat (q) is NEGATIVE

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13
Q

What is an endothermic reaction?

A

reaction where heat must be added to the system to return it to its original temperature.
quantity of heat(q) is positive

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14
Q

How are thermodynamic quantities indicated ?

A

by magnitude of change (by a number)

by direction of the flow ( + or -)

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15
Q

What are State Functions?

A

property of a system that depends on its present state (Temp and Pressure) and is independent of the previous history of the system.
TEMPERATURE is key

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16
Q

Give examples of State Functions?

A

Enthalpy

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17
Q

Define enthalpy

A 
amount of energy within a substance that can be converted to heat
Delta Hrxn = Sum Delta Hprod - Sum Delta Hreac
Enthalpy change depends on state of reactant and products
The states (gas,liquids, solid or aqueous)
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18
Q

define atom and molecule

A

single unit of an element

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19
Q

define mole

A

number of molecules in a standard amount of an element

1 mole = 32 g oxygen

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20
Q

what is avogadro’s number ?

A

number of molecules in 1 mole of oxygen

21
Q

what is atomic weight?

A

weight in grams of avogadro’s number of molecules in 1 type of atom
oxygen = 16g

22
Q

what is molecular weight?

A

weight in grams of avogadro’s number of molecules in one mole of a compound
eg HCl = 1.01g + 35.5g = 36.5g

23
Q

What is Thermodynamic standard state of a substance?

A

standard conditions
Pressure = 1 atm
Temperature = 25C

24
Q

How is standard state indicated?

A

Delta Hrxn with superscript 0

25
Q

What does constant T and P mean?

A

Constant temp and pressure means initial and final conditions are the same

26
Q

What does standard enthalpy change mean?

Delta H rxn superscript 0

A

when a specified number of moles of reactants, all STP are converted completely to the specified number of moles of products

delta H ==== change in enthalpy
0 = STP
rxn = entire reaction process

27
Q

What is standated molar enthalpy of formation ?

Delta Hf superscript 0

A

Enthalpy change for a reqction in which 1 mole of substance in a specified state is formed from its elements in their standard states.
Value is 0 for any element in its standard state

28
Q

Does magnitude of Delta H depend on amount of reactants ?

A

Yes. double reactants, doube enthalpy

29
Q

What happens if you reverse a chemical reaction?

A

results in same magnitude of enthalpy (deltaH) but opposite sign

30
Q

Define Hess’s Law

A

Heat of Reaction - Hess’ Law
enthalpy change for any reaction depends on products and reactants.
independent of the pathway or steps.

Delta Hrxn superscript 0 = Delta H a superscript 0 + Delta H b superscript…

31
Q

Bond Energies

A

amount of energy required to break and form one mole of bonds in a covalent substance in the gaseous state at Temp and Pressure

Triple bond > double bond > single bond

32
Q

What is the formula to use bond energies to estimate heat of reactions

A

FOR GAS ONLY
Delta H rxn superscript 0 =
Sum Bond Energy react - Sum Bond Energy prod

33
Q

What are the 2 cases of spontaneity of Physical and Chemical Changes

A

Spontaneous (product favoured)

Non-Spontaneous (reactant favoured)

34
Q

Define Spontaneous Physical and Chemical Changes

A

change for which the collection of products are thermodynamically MORE stable than the collection of reactants under the given conditions

35
Q

Define Non-Spontaneous Physical and Chemical Changes

A

change for which the collection of products are thermodynamically LESS stable than the collection of reactants under the given conditions
Reaction is VERY slow
Reactants are themodynamically MORE stable than the products

36
Q

What are the possible outcomes when it comes to spontaneous and non-spontaneous physical and chemical reactions ?

A

changes that are SPONTANEOUS under ALL conditions
changes that are NON-SPONTANEOUS under ALL conditions
most changes are spontaneous under SOME conditions

37
Q

What else needs to be involved in addition to enthalpy for a the direction of a spontaneous change?

A

disorder
less random&raquo_space;»> more random OR
more order&raquo_space;»> less order

38
Q

Name the types of States Functions

A

Enthalpy

Entropy

39
Q

What’s the Second Law of Thermodynamics

A

Total entropy of a system and its surroundings always increases in a spontaneous process.

Delta S system + Delta S surrounding > 0
aka rxn + system > 0

40
Q

What’s the Third Law of Thermodynamics

A

Entropy of all pure crystalline materials at absolute zero (0K) is 0 Kelvin

41
Q

What happens at absolute zero according to the Laws of Thermodynamics ?

A

no molecular motion –> no motion –> S = 04Entropy has a defined starting point

42
Q

Delta S superscript 0

A

entropy change of any substance at any condition such as 298 K
S298 superscript 0 is ALWAYS + for compounds and elements

Delta Srxn superscript 0 =
Sum n Sprod superscript 0 = Sum n Sreac superscript 0
where n = moles

43
Q

What are the processes that increase entropy?

inc disorder

A 
phase changes
   inc disorder (melting, vapourization)
   dec disorder (freezing, condensation)`
temp changes  (inc T, inc random motion)
volume changes (inc V inc random motion)
mixing of substances  H gas instead of water = mix of elements and inc disorder
inc number of particles H20 vs. H202 -- inc particles
changes in no. moles of gaseos substances
44
Q

What is free energy ?

A

energy is the capacity to do work

is DELTA S is NEGATIVE, Heat can be used to inc disorder in the system

45
Q

What is Gibbs Free Energy ?

A

indicates spontaneity of a reaction or physical change at constant T and P
Dela G = Delta H - T Delta S (at constant T and P)

46
Q

What is the relationship between Delta G and Spontaneity at constant T and P

A

Delta G is +ve —– rxn non-spontaneous and react favoured
Delta G is 0 —–reaction is at equilibrium
Delta G is -ve —– rxn is spontaneous (prod favoured)

47
Q

What is the relationship between Enthalpy, Entropy and Free Energy ?

A

G = H - TS
G— Free Energy
H — Enthalpy
S — Entropy

48
Q

When can Delta G be negative ?

A

when Delta H is negative (exothermic rxn – heat released)

When delta S is positive (greater disorder)

49
Q

What are the Delta G values?

A

Delta G superscript 0 – standard state of free energy
1 atm, 25 C, 298K)
Delta Gf superscript 0 = standard molar free energy of formation for elements in their standard state = 0

Geol 386 (6 decks)

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