Chemistry - Thermochemistry

Front 1

What is a system?

Back 1

The particular part of the universe being studied

Front 2

What is everything outside the system considered?

Back 2

It is considered the surroundings or environment

Front 3

What three things can a system be?

Back 3

It can be isolated, closed, or open

Front 4

What is an isolated system?

Back 4

It cannot exchange energy or matter with the surroundings

Front 5

What is a closed system?

Back 5

It can exchange energy but not matter with the surroundings

Front 6

What is an open system?

Back 6

It can exchange energy and matter with the surroundings

Front 7

When does a system undergo a process?

Back 7

It undergoes a process when one or more of its properties change

Front 8

What is a process associated with?

Back 8

It is associated with a change of state

Front 9

When does an isothermal process occur?

Back 9

It occurs when the temperature of the system remains constant

Front 10

When does an adiabatic process occur?

Back 10

When no heat exchange occurs

Front 11

When does an isobaric process occur?

Back 11

It occurs when the pressure of the system remains constant

Front 12

What is heat?

Back 12

It is a form of energy which can easily transfer to or from a system, the result of a temperature difference between the system and its surroundings

Front 13

What is heat absorbed by a system considered?

Back 13

It is considered positive

Front 14

What is heat lost by a system considered?

Back 14

It is considered negative

Front 15

What are reactions called that absorb heat energy?

Back 15

They are endothermic

Front 16

What are those that release heat energy?

Back 16

They are exothermic

Front 17

What is heat measured in?

Back 17

It is measured in calories or Joules and more commonly in kcal or kJ

Front 18

What is the conversion for calories to Joules?

Back 18

1 calorie is equal to 4.184 Joules

Front 19

What is the heat (q) absorbed or released in a given process calculated from?

Back 19

It is calculated from the equation q = mct

Front 20

What occurs in constant-volume calorimetry?

Back 20

The volume of the container holding the reacting mixture does not change during the course of the reaction

Front 21

What are state functions?

Back 21

They depend only on the initial and final states of the system, and not on the path of the change

Front 22

What are the state functions?

Back 22

Pressure, temperature, volume, enthalpy (H), entropy (S), free energy (G) and internal energy (E or U)

Front 23

What is the set for normal conditions?

Back 23

25C and 1atm

Front 24

What is it used for?

Back 24

It is normally used to measure enthalpy, entropy, and free energy of a reaction

Front 25

What is a substance called that is in its most stable form under standard conditions?

Back 25

It is in its standard state

Front 26

What are the changes in enthalpy, entropy, and free energy called when they occur under standard conditions?

Back 26

They are called standard enthalpy, standard entropy, and standard free energy

Front 27

What do chemists use the term enthalpy (H) for?

Back 27

They use it to express heat changes at constant pressure

Front 28

What is the change in enthalpy equal to?

Back 28

It is equal to the heat absorbed or evolved by the system at constant pressure

Front 29

To find the enthalpy change of a reaction, what do you do?

Back 29

You subtract the enthalpy of the reactants from the enthalpy of the products

Front 30

What does a positive H correspond to?

Back 30

It corresponds to an endothermic process

Front 31

What does a negative H correspond to?

Back 31

It corresponds to an exothermic process

Front 32

What is the enthalpy of formation of a compound?

Back 32

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

Front 33

What is the standard heat of reaction?

Back 33

It is the hypothetical enthalpy change that would occur if the reaction were carried out under standard conditions, ie when reactants in their standard states are converted to products in their standard states at 298K

Front 34

What does Hess’s law state?

Back 34

Hess’s law states that enthalpies of reactions are additive

Front 35

What are the heats of reaction related to?

Back 35

They are related to changes in energy associated with the break-down and formation of chemical bonds

Front 36

What is bond energy, or bond dissociation energy?

Back 36

It is the average of the energy required to break a particular type of bond in one mole of gaseous molecules

Front 37

What is entropy (S)?

Back 37

It is the measure of the disorder, or randomness, of a system

Front 38

What are the units of entropy?

Back 38

They are energy/temperature, commonly J/K or call/K

Front 39

How does order relate to entropy?

Back 39

The greater the order in a system, the lower the entropy

Front 40

Do solids have a higher or lower entropy than a gas?

Back 40

They have a lower entropy than a gas because individual molecules in the gaseous state are moving randomly, while individual molecules in a solid are constrained in place

Front 41

What does the second law of thermodynamics state?

Back 41

It states that all spontaneous processes proceed such that the entropy of the system plus its surroundings increases:

Front 42

When does a system reach its maximum entropy?

Back 42

It reaches it at equilibrium

Front 43

What does Gibbs Free Energy do?

Back 43

It combines the two factors which affect the spontaneity of a reaction

Front 44

What are the two?

Back 44

Changes in enthalpy, and changes in entropy

Front 45

What does the change in free energy of a system represent?

Back 45

It represents the maximum amount of energy released by a process, occurring at constant temperature and pressure

Front 46

What is the equation?

Back 46

G = H – TS

Front 47

What does it mean if G is negative?

Back 47

The reaction is spontaneous

Front 48

What does it mean if G is positive?

Back 48

The reaction is nonspontaneous

Front 49

What does it mean if G is zero?

Back 49

The system is at equilibrium

Front 50

If enthalpy is negative and entropy is positive, is the reaction spontaneous, when?

Back 50

It is spontaneous at all temperatures

Front 51

If the enthalpy is positive and the entropy is negative, is the reaction spontaneous, when?

Back 51

It is nonspontaneous at all temperatures

Front 52

If the enthalpy and entropy are both positive, is the reaction spontaneous, when?

Back 52

It is spontaneous only at high temperatures

Front 53

If the enthalpy and entropy are both negative, is the reaction spontaneous, when?

Back 53

It is spontaneous only at low temperatures

Front 54

What does the rate of a reaction depend upon?

Back 54

It depends upon the activation energy

Front 55

Does it depend on G?

Back 55

It does not depend on G

Front 56

What is the standard free energy

Back 56

It is defined as the G of a process occurring at 25C and 1atm pressure, and for which the concentrations of any solutions involved are 1 M

Front 57

What is the standard free energy of formation?

Back 57

It is the free-energy change that occurs when 1 mol of a compound in its standard state is formed from its elements in their standard states under standard conditions

Front 58

What is the standard free energy of formation of any element in its most stable form?

Back 58

Zero

Front 59

What is the standard free energy of reaction?

Back 59

It is the free energy change that occurs when that reaction is carried out under standard state conditions, i.e., when the reactants in their standard states are converted to the products in their standard states, at standard conditions of T and P

Front 60

What is the reaction quotient (Q)?

Back 60

It is the products raised to their amounts divided by the reactants raised to their amounts