Hammering my brain with chemistry (midterm 2)

When comparing which has lower PE, look for: (2 things)

• Phase (gas > liquid > solid)

• Bond # (more bonds = negative PE)

What makes a strong bond?

• Higher order/more bonds

• More polar

• Shorter bond length

When comparing two bonds’ attraction/repulsion graphs, what can you look for?

• Radius (small r = stronger attraction)

• Depth of curve (deeper = more negative PE = stronger attraction)

What does a low PE indicate, in regards to attraction?

Negative, strong attraction

What does a high PE indicate, in regards to attraction?

Positive, weak attraction

Exothermic reactions have what kind of ΔH(rxn)?

Negative

Endothermic reactions have what kind of ΔH(rxn)?

Positive

Exothermic reactions have (high/lower) PE and (high/low) bond energy

Lower; higher

Endothermic reactions have (high/lower) PE and (high/low) bond energy

High; low

What is ΔHf/ enthalpy of formation?

Heat energy released/consumed when 1 mol of substance is formed from pure elements in stable form/standard state

What is important to remember about ΔHf and pure elements?

Pure elements have an ΔHf of 0

When comparing ΔS/entropy, what can you look at?

• Phase of matter

  • # of particles if both liquid

  • Heat if both solid

• # of molecules

• Spread

What is the sign of a spontaneous reaction ΔStot?

Positive

What is the sign of a nonspontaneous reaction ΔStot?

Negative

What is the sign of a spontaneous ΔG?

Negative

What is the sign of a nonspontaneous ΔG?

Positive

Characterize spontaneous reactions on the following criteria:

• (Product/reactant) favored

• (Endergonic/exergonic)

• Likely to (gain/lose) e

• (Reduction/oxidation)

• Product favored

• exergonic

• Likely to gain e

• Reduction

Characterize nonspontaneous reactions on the following criteria:

• (Product/reactant) favored

• (Endergonic/exergonic)

• Likely to (gain/lose) e

• (Reduction/oxidation)

• Reactant favored

• Endergonic

• Likely to lose e

• Oxidation

What is the sign of a spontaneous E?

Positive

What is the sign of a nonspontaneous E?

Negative

How can you predict sign of ΔHsys?

Strength of attractions (bond and IMF strength)

Strong = negative

Weak = positive

How can you predict the sign of ΔSsurr?

Opposite sign of ΔHsys

How can you predict the sign of ΔSsys?

Phases of matter

What does ΔE indicate?

Tendency of a chemical species to gain electrons and be reduced

What does ΔG indicate?

Spontaneity

What does ΔS indicate?

Entropy, spread of energy/matter, number of ways to arrange a system

What does ΔH indicate?

Enthalpy, heat

What are the characteristics of a cathode?

• (Oxidation/reduction) side

• (Gains/loses) e

• (Lower/higher) E

• (Anion/cations) added

• Reduction side

• Gains e

• Higher E

• Cations added

What are the characteristics of an anode?

• (Oxidation/reduction) side

• (Gains/loses) e

• (Lower/higher) E

• (Anion/cations) added

• Oxidation side

• Loses e

• Lower E

• Anions added

Work equation, distance and force

w = d x f

Work equation, pressure and volume

w = -P_extΔV

Work equation, m g and ΔH

w = mgΔH = PE

Efficiency equation

w/q (100)

-ΔH and +ΔS is spontaneous at what temp?

All temps

-ΔH and -ΔS is spontaneous at what temp?

Low temps

+ΔH and -ΔS is spontaneous at what temp?

No temps

+ΔH and +ΔS is spontaneous at what temp?

High temperatures

ΔG equation with Faraday’s constant and E

ΔG = -nFE

where n is # of electrons in reaction

F = 96.5

What sign is ΔH if endothermic?

Positive

ΔH > 0

What sign is ΔH if exothermic?

Negative

ΔH < 0