Thermochemistry

Question 1

Isolated system:

Answer 1

cannot exchange energy (heat and work) or matter with surroundings.

Question 2

Closed system

Answer 2

can exchanges energy (heat and work) but not matter with surroundings.

ex: an steam radiator, sealed container with hot liquid.

Question 3

Open system

Answer 3

can exchange both energy and matter with surroundings.

ex: pot of boiling water

Question 4

First law of thermodynamics

Answer 4

change in U (internal energy) = Q(heat added) - W(work done by the system.

Question 5

What is the effect of an isovolumetric process on internal energy and why?

Answer 5

internal energy=Q(heat) because if there is no change in the volume of a gas it does not perform any work.

Question 6

What is coupling?

Answer 6

An exergonic reaction is paired with an endergonic reaction so that the exergonic reaction’s energy release will provide the energy needed for the endergonic reaction.

Question 7

Standard states

Answer 7

most stable form of a substance under standard conditions (25C/298K, 1atm, 1M)
H2 gas
H2O liquid
NaCl solid
O2 gas
C slid graphite

Question 8

What terms are used for determining the heat exchanges at phase changes?

Answer 8

solid-liquid boundary uses change in heat (enthalpy) of fusion (+ if melting, - if freezing)

liquid-gas boundary uses enthalpy of vaporization (+ if evaporating, - is condensation is occurring.)

Question 9

What equation is used to determine the heat or enthalpy released or absorbed by a process?

Answer 9

q=mc(delta)T
m=mass, c=specific heat
For an adiabatic system (no heat exchange between system and environment):
q (system) = -q (surroundings)

Question 10

What is enthalpy?
How do you calculate enthalpy of a reaction?
What does a +/- enthalpy of a reaction indicate?

Answer 10

heat changes in a system with constant pressure
H(rxn) = H (products) - H (reactants)
+H = endothermic reaction
-H = exothermic reaction

Question 11

Hess’s Law

Answer 11

total change in PE of a system = sum of changes of PE in each individual step

Question 12

Gibbs free energy

Answer 12

change in G (entropy) = change in H (enthalpy) - T x change in S (entropy)

Question 13

standard free energy

hw does Keq affect free energy?

Answer 13

standard free energy = -RTlnKeq

greater Keq = greater ln of Keq = more negative free energy change