Thermodynamics 2

Question 1

What is heat capacity (C) ?

Answer 1

• The amount of heat required to raise the temperature of an object or substance a given amount by 1°C.

Question 2

What is Molar Heat Capacity (Cm) ?

Answer 2

• The amount of heat required to raise the temperature of 1 mol of a substance by 1 °C

Question 3

Calorimetry and Heat Capacity

Answer 3

• Measure the heat flow at constant volume (∆E).

Question 4

Heat capacity equation

Answer 4

q = C x ∆T (q: quantity of heat)

Question 5

Molar Heat Capacity (Cm) equation

Answer 5

q = (Cm) x (moles of substance) x ∆T

Question 6

What is specific heat ?

Answer 6

• The amount of heat required to raise the temperature of 1 g of a substance by 1 °C.

Question 7

Specific heat equation

Answer 7

• q = (specific heat) x (mass of substance) x ∆T

Question 8

Differential Scanning Calorimetry
(DSC)

Answer 8

• measures difference in heat transferred to
  and from sample in comparison to reference material

Question 9

Hess’s law

Answer 9

• The overall enthalpy change for a reaction is equal to the sum of the enthalpy changes for the individual steps in the reaction

Question 10

Haber Process

Answer 10

• 3H2(g) + N2(g) 2NH3(g)
• ∆H° = -92.2 kJ

Question 11

Standard Enthalpy of Formation (ΔH0)

Answer 11

• the heat change that results when one mole of a compound is formed from its elements at a pressure of 1 atm

Question 12

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

Answer 12

• the standard enthalpy of formation of any element in its most stable form is zero.

Question 13

Standard Heat of Formation (∆H°f )

Answer 13

• enthalpy change for the formation of 1 mol of a substance in its standard state from its constituent elements in their standard states

Question 14

Is breaking bonds (dissociation) endothermic or exothermic ?

Answer 14

• endothermic

Question 15

Is making new bonds (association) endothermic or exothermic ?

Answer 15

• exothermic

Question 16

Bond Dissociation Energy

Answer 16

• amount of energy that must be supplied to break a chemical bond in an isolated molecule in the gaseous state
• thus the amount of energy released when the bond forms

Question 17

What do exact bond enthalpy values depend on ?

Answer 17

• bond order
• electronic environment of the 2 atoms compromising the bond

Question 18

Equation for calculating ΔH using bond enthalpies ?

Answer 18

• ΔH = Bonds Broken − Bonds Formed

Question 19

Standard Enthalpies of Combustion, ΔHc

Answer 19

• Standard change in enthalpy per mole of combustible substance

Question 20

Equation for calculating standard enthalpies of combustion ?

Answer 20

• ΔH = Bonds Broken − Bonds Formed
• arrows go down

Question 21

What is a spontaneous processes ?

Answer 21

• A process that, once started, proceeds on its own without a continuous external influence.

Question 22

18–20-year-old males require…..

Answer 22

~12 MJ of energy input per day.

Question 23

18–20-year-old females require

Answer 23

~9 MJ of energy input per day.

Question 24

What is body temperature regulated by?

Answer 24

• radiation and perspiration.

Question 25

State Function

Answer 25

• A function or property whose value depends
  only on the present state, or condition, of the system, not on the path used to arrive at that state.

Question 26

Enthalpy Change (ΔH)

Answer 26

-The heat change in a reaction or process at constant pressure; ΔH = ΔE + PΔV.

Question 27

Entropy (S)

Answer 27

• The amount of molecular randomness in a system

Question 28

What are spontaneous processes favoured by?

Answer 28

• Favoured by a decrease in H (negative ∆H).
• Favoured by an increase in S (positive ∆S).

Question 29

What are non spontaneous processes favoured by?

Answer 29

• Favoured by an increase in H (positive ∆H).
• Favoured by a decrease in S (negative ∆S).