CHEM 162 exam 3 content

What’s Enthalpy’s general formula?

H = E + (P x V)

What’s ΔE?

q + (-P ΔV)

What’s ΔH equal if pressure is held constant?

q

ΔH is?

H final - H initial

what’s q equal to in relation to ΔH?

q = ΔH = (moles reacted) X ΔHrxn

If ΔH is negative then?

system cools down —> exo

If ΔH is positive then?

system heats up —> endo

ΔH is specific to the amount of?

reaction (moles)

Answer Question

C, because the reaction starts at high and ends in low. The system is losing energy.

What’s A? is it Endo or Exo?

Melting/Fusion

• Endo

What’s B? Is it Endo or Exo?

Freezing

• Exo

What’s C? is it Endo or Exo?

Sublimation

• Endo

What’s D? is it Endo or Exo?

Deposition

• Exo

What’s E? is it Endo or Exo?

Evaporation

• Endo

What’s F? is it Endo or Exo?

Condensation

• Exo

1. A

2. D

3. A

4. A

5. A

6. D

7. A

What’s A-E show in phases?

A. Soild

B. Solid → liquid

C. Liquid

D. liquid → gas

E. gas

What does the line C represent?

Phase

What does the line D represent

phase change

What formula would you need to use for line C & why?

q= m * cp * ΔT

• in phase

What formula do you need to use for D & Why?

q= n * ΔH

• because phase is changing

During the duration of a reaction the q total (heat total) will equal

q1 + q2 + qn (n = amount of times heat changes in corresponding phases)

When Temperature changes what happens to KE?

Changes

When temperature is constant what happens to KE?

KE is constant

PE changes when?

phases changes (flat graph: temperature constant))

PE doesn’t change when?

in phase (slop graph: temperature changing)

What is the 2 rules for manipulating reactions?

1. if you flip reactions (making the reactants to products instead) you must change the sign of ΔH

2. What you multiply reaction by is what you multi ΔH by.