Enthalpy and heat of reaction

Question 1

What is heat?

Answer 1

disorganised, random movement

Question 2

What is work?

Answer 2

Organised in one direction

Question 3

What is a state function?

Answer 3

Quantity that depends only on the thermodynamic state of the system and not on how that state was prepared

Question 4

What are examples of state functions?

Answer 4

H, U , Cvm and Cpm

Question 5

What are not state functions?

Answer 5

Heat and work

Question 6

What is the equation for enthalpy?

Answer 6

H = U + pV 
(Enthalpy = energy + (pressure x volume)

Question 7

What is the equation for enthalpy at a constant pressure?

Answer 7

ΔH = ΔU + pΔV

Question 8

How does ΔH relate to first law?

Answer 8

ΔH = q + w = q - pΔV

Question 9

What is the change in enthalpy for a reactant at a constant pressure is equal to?

Answer 9

Heat

(ΔH)p = q

Question 10

What is the change in enthalpy for a reactant at a constant volume equal to?

Answer 10

Heat

(ΔH)v = q

Question 11

What is the molar heat capacity?

Answer 11

The heat required to raise the temperature of one mole of substance by one kelvin

Question 12

What is the equation for molar heat capacity at a constant volume?

Answer 12

Cvm = (δUm / δT)v

Question 13

What is the equation for the molar heat capacity at a constant pressure?

Answer 13

Cpm = (ΔHm/δT)p

Question 14

What does “m” mean in the molar heat capacity equations?

Answer 14

Per mole

Question 15

What is the equation for a slope?

Answer 15

Δy / Δx

Question 16

If Δx = 0, what can you write the exact slope as?

Answer 16

δy / δx

Question 17

What can you do if y depends on another variable z as well as x?

Answer 17

Specify the slope in the direction of constant Z as (δy/δx)ᴢ

Question 18

What principle does calorimetry run on?

Answer 18

If water gains heat, the chemical system must have lost heat

Question 19

What is ΔғH?

Answer 19

The standard enthalpy of formation

Question 20

What is the definition of the standard enthalpy of formation?

Answer 20

The enthalpy change when one mole of substance is made from its elements in their reference states

Question 21

What is ΔrxnH?

Answer 21

Enthalpy of reaction

Question 22

How do you calculate enthalpy of reaction?

Answer 22

ΔrxnH = Σ vΔfH (products) - Σ vΔfH (reactants)

Question 23

What do you need to take into account when you work out ΔrxnH?

Answer 23

The stochiometry of the reaction

Question 24

What does Kirchoff’s law describe?

Answer 24

Describes the enthalpy of a reaction’s variation with temperature changes

Question 25

What is the equation for Kirchoff’s law?

Answer 25

ΔrxnH° (T2) = ΔrxnH° (T1) + ΔrxnCp (T2-T1)

Question 26

How do you calculate ΔrxnCp?

Answer 26

ΔrxnCp = ΣvCp,m (products) - ΣvCp,m (reactants)

Question 27

What does Kirchhoff’s law assume?

Answer 27

Heat capacities don’t change with temperature