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Combusion > Thermochemistry Review > Flashcards

Thermochemistry Review Flashcards

1
Q

What is the focus of thermochemistry?

A

To determine how energy is “transferred” during chemical reactions.

Rogers, Chem for Eng., Pg 119

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2
Q

Enthalpy help to understand _______ energy is transferred.

A

how

Rogers, Chem for Eng., Pg 119

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3
Q

Entropy helps to understand _______ energy is transferred.

A

Why

Rogers, Chem for Eng., Pg 119

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4
Q

Free energy helps to understand _____ energy is transferred.

A

when

Rogers, Chem for Eng., Pg 119

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5
Q

What is the SI definition of a Joule?

A

1J = kg*m^2/s^2

Rogers, Chem for Eng., Pg 120

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6
Q

What is the english unit for energy used in chemical TD?

A

The calorie

Rogers, Chem for Eng., Pg 120

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7
Q

What is the conversion from calories to joules? Is it exact?

A

1 cal = 4.184 J
Yes, it is exact by definition.

Note: 1Cal = 1000 cal

Rogers, Chem for Eng., Pg 120

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8
Q

Conceptually describe the internal energy of an arbitrary system?

A

The internal energy of a system represents the total kinetic and potential energy of every particle in the system.

Rogers, Chem for Eng., Pg 121

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9
Q

True or False
The actual internal energy (E) of a system is often unknowable. However, we can often determine how the system changes (Delta E).

A

True.

Rogers, Chem for Eng., Pg 120

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10
Q

If Delta E is positive, the system has ____ energy. If Delta E is negative the system has ______ energy.

A

Gained
Lost

Rogers, Chem for Eng., Pg 122

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11
Q

What is the first law of thermodynamics?

A

Energy cannot be created or destroyed; it can only be converted from one form to another. Therefore the total energy in any system is constant.

Rogers, Chem for Eng., Pg 122`

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12
Q

True or False

Any energy lost by the system must be gained by the surroundings.

A

True

Rogers, Chem for Eng., Pg 123

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13
Q

What is the general definition of energy?

Define conceptually

A

The capacity to do work or transfer heat.

Rogers, Chem for Eng., Pg 123

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14
Q

What are the two ways that a system can transfer energy?

A

Heat and work.

Rogers, Chem for Eng., Pg 123

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15
Q

Delta E = ___ + ______

A

q + w

Where q is heat and w is work.

Rogers, Chem for Eng., Pg 123

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16
Q

What is the conceptual definition of heat?

A

The flow of energy that occurs as a result of a difference in temperature.

Rogers, Chem for Eng., Pg 123

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17
Q

True or False

Heat is energy.

A

False. Heat is a way energy can be transferred.

Rogers, Chem for Eng., Pg 123

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18
Q

What is the conceptual definition of work?

A

Work is the result of a force acting through a distance.

Rogers, Chem for Eng., Pg 123

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19
Q

In chemical thermodynamics, the signs of heat and work are determined from the point of view of ______.

A

The system.

Rogers, Chem for Eng., Pg 124

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20
Q

If energy in the form of heat flows from the surroundings into the system q is ______.

A

Positive.

Rogers, Chem for Eng., Pg 124

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21
Q

If energy in the form of heat flows out of the system into the surroundings, q is _______.

A

Negative.

Rogers, Chem for Eng., Pg 124

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22
Q

If the surroundings do work on the system, w is ______.

A

Positive.

Rogers, Chem for Eng., Pg 124

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23
Q

If the system does work on the surroundings, w is ______.

A

Negative.

Rogers, Chem for Eng., Pg 124

24
Q

What is pressure-volume work?

A

Work done in open containers under constant pressure conditions.

Rogers, Chem for Eng., Pg 124

25
Q

A piston compressing a fixed amount of gas in a cylinder would be an example of ___ work.

A

pV (pressure-volume)

Rogers, Chem for Eng., Pg 124

26
Q

What is a state function?

A

A state function is a property of a system that is determined by specifying the state or condition of the system.

State functions deal with properties of the system that are path independent.

Rogers, Chem for Eng., Pg 126

27
Q

True or False

A state function is dependent on the history of the system.

A

False. A state function is independent of the history of the system. In other words, a state function does not depend on the pathway followed to get to the current state.

Rogers, Chem for Eng., Pg 126

28
Q

What are some examples of state functions used in chemical analysis?

A

Pressure, temperature, concentration, and volume.

Rogers, Chem for Eng., Pg 126

29
Q

True or False

Heat and work are state functions.

A

False. Heat and work are not state functions. They are path dependent.

Rogers, Chem for Eng., Pg 126

30
Q

What is the conceptual definition of heat capacity?

A

Heat capacity is defined as the amount of heat required to raise the temperature of a substance by 1 unit degree.

Rogers, Chem for Eng., Pg 129

31
Q

Heat capacity is an _____ property.

A

Extensive

Rogers, Chem for Eng., Pg 129

32
Q

What is the conceptual definition of specific heat capacity (also just called specific heat)?

A

Specific heat capacity is the mass normalized heat capacity.

Rogers, Chem for Eng., Pg 129

33
Q

What are the SI units for specific heat?

A

MLT System: L^2/(Theta-T^2)

Jkg^-1K^-1 (Mostly used in Chem)
or
Jg^-1K^-1 (Mostly used in TD)

Rogers, Chem for Eng., Pg 129

34
Q

What is a simple conversion equation between energy and pressure?

A

101.3 J == 1 L*atm

Where L is liters

Rogers, Chem for Eng., Pg 128

35
Q

What is the molar heat capacity?

A

The amount of heat required to raise the temperature of 1 mole of a substance by 1 degree Celsius.

In other words its the mole normalized heat capacity.

Rogers, Chem for Eng., Pg 130

36
Q

What is the specific heat of water in liquid form?

Units J/(g*degrees C

A

4.18 J/(g*degC)

Rogers, Chem for Eng., Pg 130

37
Q

For the change in energy of a system under constant volume conditions how is energy transferred?

A

The only way that energy can be transferred is in the form of heat. No work can be done since the volume does not change.

Rogers, Chem for Eng., Pg 135

38
Q

Under constant pressure conditions, the change in _____ equals the energy flow as heat.

A

enthalpy (Delta H)

Rogers, Chem for Eng., Pg 135

39
Q

Give three reasons why measuring the change in enthalpy is useful.

A
  1. Entropy allows us to describe the energy of the system without having to measure work.
  2. For most reactions the change in enthalpy is very close to the change in energy.
  3. There is a vital relationship between enthalpy and entropy.

Rogers, Chem for Eng., Pg 135

40
Q

If a chemical reaction releases heat it is referred to as ______.

A

Exothermic.

Rogers, Chem for Eng., Pg 135

41
Q

If a chemical reaction absorbs heat the reaction is considered ________.

A

Endothermic.

Rogers, Chem for Eng., Pg 135

42
Q

For an exothermic reaction, what is the sign of the change in enthalpy?

A

Negative. (<0)

Rogers, Chem for Eng., Pg 136

43
Q

For an endothermic reaction, what is the sign of the change in enthalpy?

A

Positive (>0).

Rogers, Chem for Eng., Pg 136

44
Q

All combustion reactions are _________.

A

Exothermic.

Rogers, Chem for Eng., Pg 136

45
Q

For an exothermic reaction, heat can be considered a_____ of the reaction.

A

Product.

Rogers, Chem for Eng., Pg 136

46
Q

For an endothermic reaction, heat can be considered a ________.

A

Reactant.

Rogers, Chem for Eng., Pg 136

47
Q

What is a thermal chemical equation?

A

A thermal chemical equation is a balanced equation that includes the enthalpy change for the reaction.

Rogers, Chem for Eng., Pg 138

48
Q

What are the three conditions for a thermodynamic standard state?

A
  1. Every solid liquid and gas is in its pure form at 1 atm of pressure.
  2. Every solute in a solution has a concentration of 1 M.
  3. The temp is at 25 degrees C.

Rogers, Chem for Eng., Pg 138

49
Q

Define the standard enthalpy of reaction.

A

The standard enthalpy of reaction, is defined as the enthalpy change that occurs when all of the reactants and products are in their standard states.

Rogers, Chem for Eng., Pg 138

50
Q

The° that is used in the symbol for the standard enthalpy of reaction is used to specify _______.

A

The reaction occurs under standard conditions.

Rogers, Chem for Eng., Pg 138

51
Q

If the equation is reversed how does the sign of the standard enthalpy of reaction change?

A

It flips sign.

Rogers, Chem for Eng., Pg 138

52
Q

True or false
The enthalpy of reaction is for the number of moles of reactants and products that are specified by the coefficients in the equation.

A

True. This is the third rule of using Thermochemical equations.

Rogers, Chem for Eng., Pg 138

53
Q

What are the units for a change in enthalpy?

A

Joules.

Rogers, Chem for Eng., Pg 139

54
Q

True or False

Delta H is a state function.

A

True.

Rogers, Chem for Eng., Pg 141

55
Q

State Hess’s law.

A

The total enthalpy change for a process is the same regardless of whether it occurs in one step or in many.

Rogers, Chem for Eng., Pg 141

56
Q

Define standard enthalpy of formation.

A

The standard enthalpy of formation, ΔH_f^°, is the standard enthalpy change that occurs when one mole of a substance is formed from its elements in their most stable form.

Rogers, Chem for Eng., Pg 143

57
Q

What is the standard enthalpy of formation for an element in its most stable form?

A

Zero.

Rogers, Chem for Eng., Pg 144

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