Thermochemistry Chapter 9 Lecture 3

Question 1

Thermodynamic state of a system

Answer 1

Specifying values of a set of measurable properties sufficient to determine all other properties.
e.g. n, P, and T determine states of an ideal gas. V=nRT/P d=m/v = nM/v = PM/RT

Question 2

State function

Answer 2

unique value for a specified state of a system.

Question 3

State function: Extensive examples

Answer 3

Volume, Mass, Internal Energy, Enthalpy

Question 4

State function Intensive

Answer 4

Density, Pressure, Temperature

Question 5

Path dependent Extensive

Answer 5

Heat, Work

Question 6

Path dependent Intensive

Answer 6

Heat, Capacity

Question 7

First Law of Thermodynamics

Answer 7

(Uf-Ui) = q + w = q -P (Vf-Vi)
Change in the internal energy of the closed system (U) is equal to the amount of work + heat supplied to the system.

Question 8

Enthalpy H

Answer 8

Extensive state function that is the sum of the internal energy and pressure-volume product: H = U + PV or (Hf-Hi) = (Uf-Ui) + P(Vf-Vi)

Question 9

What happens when there is constant pressure for Enthalpy?

Answer 9

Only heat can be gained or loss by function H=qp

Question 10

Standard Enthalpy of reaction

Answer 10

(Hrxn) Change that occurs when all the reactants and products are in standard states.
Examples:
Gas: pure gas at 1 atm
liquid: pure liquid at 1 atm
Solid: pure solid at 1 atm
Solute: At concentration of 1M (mole/liter)

Question 11

Hess’s law

Answer 11

Total enthalpy change = reaction is the sum of all changes

Question 12

Standard Enthalpy of formation

Answer 12

(Hf) is enthalpy change in the formation of one mole of a substance in the standard state from the reference forms of its elements in standard states.
Ex: (Hf) of H2O(l) = -285.8 Kj/ mol

Question 13

Allotropes

Answer 13

Different structured form of elements within the same physical state:
Ex: O2 & O3

Question 14

what does it mean for (Hf-Hi)<0

Answer 14

They are stable because the enthalpy of a compound that is lower than the constitute elements and its decomposition need energy input as heat.
Usually exothermic rxns

Question 15

what does it mean for (Hf-Hi)>0

Answer 15

They are less stable because when they are greater than constitute elements, they release heat upon decomposition.

Question 16

How can you calculate the change in Enthalpy?

Answer 16

Subtract the Enthalpies formation that are in the product from the enthalpy’s formation in reactant side
Product- Reactant = (Hf-Hi)

Question 17

Exothermic reactions in relation to Q

Answer 17

They are overall having a negative enthalpy reaction and q is negative because it exits the system.

Question 18

why is change in G >0 equal product in favored?

Answer 18

If G < 0 they are stable enough for reactants to turn into products the inverse happens if G <0

Question 19

what are the rules of S universe in relation to 0?

Answer 19

Suniv > 0 = product is favored
Suniv < 0 = reactant is favored
Cause less entropy overall means the reactant was probably better in having more randomness.

Question 20

If the surrounding is doing work on the system in chemical reaction

Answer 20

The moles of gas decrease

Question 21

What happens when chemical energy increases?

Answer 21

Chemical bonds break down.

Question 22

Finding Enthalpy vaporization

Answer 22

Hvap = (-R ln ( P2/P1) )/ 1/T2 - 1/T1

Question 23

Finding Pressure

Answer 23

P2 = P1 e^ Hvap/R (1/T2 - 1/T1)

Question 24

Constant of mole —> L

Answer 24

1mole =22.4L

Question 25

Finding Temp change in Hvap

Answer 25

T2= [1/T1 - Rln(P2/P1)/Hvap)^-1