Thermodynamics Flashcards

1
Q

In a piston, as gas is expanding, does the gas heat or cool?

A

The gas cools as it expands.
Because the gas/our system is doing work when it expands, the system loses energy. And because internal energy is proportional to temperature, the gas will cool.

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2
Q

In a piston, as a gas is being compressed, is it gaining internal energy or releasing internal energy?

A

Gains internal energy.

Work is being done on the system by the surrounding, so internal energy increases and gas warms as it is compressed.

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3
Q

Expanding gases cool or warm?

A

Cool

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4
Q

Compressed gas cools or warm?

A

Warm

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5
Q

What is the first law of thermodynamics?

A

total energy of universe is constant

Delta(E) = q + w

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6
Q

When is q(heat) positive or negative?

A
q = + when system gains heat/energy
q = - when system loses heat/energy
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7
Q

When is W(work) positive or negative?

A
W = + when work id done on system by surrounding
W = - when work is done by system
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8
Q

Does change in enthalpy depend on the pathway of a reaction?

A

Nope! It only depends on final and initial values.

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9
Q

What is the difference between standard state conditions and stnadard temperature and pressure (STP)?

A

Standard state is when T = 298 K (25 degrees Celsius) and P = 1 atm and all solids and liquids are assumed to be pure and concentrations are assumed to be at 1 M, values determined at standard state have a superscript (like a degree sign)

STP is when T = 273 K (O degrees Celsius!!!)

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10
Q

Examples of elements in their natural or standard state, so heat of formation equals 0

A

C(s), graphite
O2
H2
Cl2

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11
Q

What are the standard states of the halides?

A

F2 (g)
Cl2 (g)
Br2 (l)
I2 (s)

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12
Q

When H = + and S = -, what is G? Is the reaction spontaneous?

A

G is positive and reaction is not spontaneous.

Think of it this way, H = + means it’s endothermic and requires more energy to break a bond than the energy released, that is not very favorable because you want a final product with a lower energy state so it will release energy. The 2nd law of thermodynamics also says that disorder if favored, that mean S = - is not as favorable because it would be a decrease in entropy

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13
Q

At high temperatures with H = + and S = +, is the reaction spontaneous?

A

Reaction is spontaneous and G is negative.

This is because higher temperatures makes entropy (S) have a bigger effect on G, so during high temperatures, G will follow what S is.

At low temperatures, S has little effect and you pay attention more to what H likes.

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14
Q

When equilibrium constant equals 1, reaction is driven by?

A

Le Chatelier’s Principles because at equilibrium, the concentration of products is equal to the concentration of reactants

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15
Q

What is the difference between deltaG and deltaG°?

A

deltaG tells you if a reaction will be spontaneous in one direction or the other direction, this value is affected by changing reaction composition until it reaches 0, equilibrium

deltaG° is the relative proportions of products and reactants present at equilibrium, at constant temperatures this value is constant

deltaG = deltaG° + RTlinQ
deltaG° = - RTlnKeq
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16
Q

What is happening during an adiabatic process?

A

No heat is exchanged between the system and surrounding so q = 0 and the change in internal energy of the system is equal to the work done. If a gas is compressed, work is being done on the gas so that would lead to a positive W and positive internal energy which is correlated with temperature so the temperature will increase.

17
Q

How is heat and moles related to enthalpy?

A

deltaH = q/n [J/mol]