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Thermochemisty Flashcards

1
Q

What are the two types of energy?

A

Kinetic and potential energy

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2
Q

What is kinetic energy?

A

The energy in motion, = 3/2(RT)

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3
Q

What is potential energy?

A

Stored energy due to position. = mgh

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4
Q

What is internal energy?

A

Internal energy is the sum of KE and PE of all components of the system, or the capacity of a system to do work or transfer heat.

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5
Q

Change in internal energy (U)

A

change in U = U(products) - U(reactants). It is also the sum of energy transferred to/from the surroundings in the form of heat and work (change in U = q + w)

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6
Q

What are the two ways to transfer energy?

A

Heat(q) and work(w)

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7
Q

What is work (w)

A

It is energy transfer (moving mass) that causes a mass to be moved by applying a force. = force*distance. A state DEpendent function (path function).

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8
Q

What is heat (q)

A

It is energy transfer (energy difference) that causes an increase in temperature until thermal equilibrium. A state DEpendent function (path function).

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9
Q

What is the system?

A

The item of interest for which we track energy changes. The values and signs for U, q, and w refer to the system. Energy into: positive. Energy out: negative.

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10
Q

What is the surroundings?

A

Everything in the universe that is not the item of interest (system.) Most observations are made in the surroundings.

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11
Q

What happens when q < 0?

A

The system transfers heat to the surroundings (leaves system).

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12
Q

What happens when q > 0?

A

The surroundings transfer heat to the system (enters system).

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13
Q

What happens when w < 0?

A

The system does work on the surroundings (system spends energy).

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14
Q

What happens when w > 0?

A

The surroundings do work on the system (system gains energy).

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15
Q

What is an open system?

A

A system that exchanges both matter and energy with the surroundings. Living beings are open systems, ecosystems.

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16
Q

What is a closed system?

A

A system that exchanges only energy (q & w, or q or w) with the surroundings, ex. greenhouse.

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17
Q

What is a isolated system?

A

A system that exchanges neither energy or matter with the surroundings.

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18
Q

What is heat transfer proportional to?

A

It is proportional to temperature change.

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19
Q

What is heat transfer?

A

Objects will exchange heat until they reach thermal equilibrium.

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20
Q

What is thermal equilibrium?

A

Thermal equilibrium is reached when objects share the same final temperature.

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21
Q

What is the work done by gas equivalent to?

A

The area under the plot of P*V is the work done by the gas. Pressure is constant because it is the external atmospheric pressure.

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22
Q

What is a state function?

A

A state function is path independent, and the overall change depends only on initial and final states. They are properties of the system. T, P, V, U, & PE are state functions.

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23
Q

What is a path function?

A

Properties of the path from the initial to the final state. (q & w).

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24
Q

What is the first law of thermodynamics?

A

The total energy of the universe is conserved (system & surroundings). Energy is not created or destroyed, and any energy lost by the system is gained by the surroundings. So, +change in U (system) = -change in U (surroundings.)

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25
What is the heat exchange measured at constant volume equal to?
q = change in internal energy. Since the change in the volume is a constant (0), w = -P*(change in volume) = 0. So, change in U = q + w where w = 0.
26
What is a bomb calorimeter?
It measures changes in internal energy of reactions at constant volume.
27
What happens in a bomb calorimeter experiment?
In the experiment, the system is only the chemical reaction. The actual calorimeter is part of the surroundings. Heat flows between the reaction and calorimeter.
28
What is the equation for the bomb calorimeter?
q(cal) = -q(rxn), and q(cal) = C(cal)*change in temp(cal), where C is the calorimeter constant.
29
What is a coffee cup calorimeter?
A coffee cup calorimeter measures heat flow at constant pressure, q(p). Heat flows between the reaction and solution. Heat from reaction (system) will change the temperature of certain mass of solution, so here the change in internal energy does not equal the heat of pressure.
30
What is the equation of the coffee cup calorimeter?
q(soln) = (specific heat capacity)(mass of solution)(change in temperature)
31
What is the thermodynamic quantity for heat exchange at constant pressure?
Enthalpy, which is a state function as it is defined of U, P, and V as: H = U + PV
32
What is the change in enthalpy equal to?
The change in enthalpy is equal to heat at constant pressure.
33
What is specific heat capacity?
The amount of heat needed to raise the temperature of 1g of a substance by 1 c or 1 K. Calculated by q = c*m*change in temp
34
What is molar heat capacity?
It is the amount of heat required to raise temperature of 1 mol of a substance by 1 C or 1 K. Calculated by q = c*n*change in temp
35
What is the heat capacity of metals?
Metals have very low heat capacity as they are easy to heat up.
36
What is the heat capacity of water?
Water has very high head capacity, and can store a lot of heat due to H-bonds that are hard to break.
37
What is the measured heat exchange equal to?
It is equal to the changes in different state functions of the system, depending on the conditions.
38
Heat flow at constant volume gives...?
Change in internal energy
39
Heat flow at constant pressure gives...?
Change in enthalpy
40
What are the enthalpies of phase changes?
They are changes in physical state, with no change in composition. Each phase change involves a change in the energy of the system.
41
What are the endothermic processes (absorb heat)?
Fusion (melting), vaporization, sublimation
42
What are the exothermic processes (release heat)?
Freezing, condensation, deposition
43
What are the ways that magnitude of change in enthalpy phase change is determined by?
The strength of intermolecular forces and the phases involved.
44
What does the changeH(sub) equal to?
changeH(vap) + changeH(fus)
45
What does the changeH(endo) equal to?
-changeH(exo)
46
What are tabulated enthalpies of phase changes?
They are molar quantities, enthalpy changes per mol of substances.
47
What are the enthalpy of fusion and vaporization measured by?
Measured at the normal melting and boiling points respectively.
48
What are the two processes identified in the heating curve?
Phase change and the heating of the substance
49
What is phase change in terms of added heat?
Added heat does not change the temperature (constant)
50
What is the heating of the substance in terms of added heat?
Added heat changes temperature between phase changes
51
What is the equation for the enthalpy of reaction?
deltaH(rnx) = SUMH(products) - SUMH(reactants)
52
What is a thermochemical equation?
The balanced chemical equation that includes the value of deltaH. It provides the relationship between the amounts of chemicals and enthalpy change in the reaction.
53
What are the three things that thermochemical equations depend on?
1) Magnitude of deltaH depends on amounts of reactants and products. 2) deltaH forward = -deltaH reverse. 3) deltaH depends on the physical state of reactants and products.
54
What is the standard state pressure in CHEM 102?
1 ATM
55
What is the standard state temperature in CHEM 102?
25 C, 298 K
56
What is the standard enthalpy of formation?
The enthalpy change for the (hypothetical) formation of 1 mol of substance in its thermodynamic state from its constituent elements in their standard states.
57
How can you use the enthalpies of formation to calculate the enthalpies of reaction steps?
1) Decompose reactants into elements. 2) Recombine elements into products
58
What is the enthalpy calculation equation?
deltaH(rxn) = SUM(nu products)deltaHf(products) - SUM(nu reactants)deltaHf(reactants)
59
What does nu stand for?
Unitless stoichiometric coefficients in the reaction equation
60
What are reactions a defense against in the atmosphere?
They are an outer defense against radiation and high energy particles, they absorb chemical radiation
61
What is photodissociation?
Molecules absorb photons and bonds are broken, incoming energy must be sufficient to break a bond.
62
What does photodissociation increase with? (kJ/mol)
Increase with bond strength
63
What is photoionization?
Molecule absorbs photons and loses electrons, so ions are formed. The photon must have enough energy to remove an electron
64
What is stronger, photoionization or photodissociation?
Photoionization takes more energy than photodissociation because shorter wavelength photons are filtered. Shorter wavelength = higher energy
65

Chem 102 (3 decks)

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