Chem 116 Exam 4 WVU

What does ∆S⁰ < 0 mean?

• Entropy/disorder is DECREASING

• ∆S⁰ is negative

Which factors INCREASE entropy? ∆S⁰ > 0

• MORE particles forming

• A solid turning into a liquid or gas. A liquid turning into a gas.

• A mixture being combined into the same area

What’s the formula for Δ S⁰_rxn?

ΔS_rxn∘​=∑νi​S_products∘​−∑νi​S_reactants​∘

vi = Stoichiometric coefficient for that substance

What’s Gibbs Free Energy equation?

ΔG=ΔH−TΔS

ΔH: Enthalpy change (essentially the sum of energy and pressure in a system)

T: Temperature in Kelvin

ΔS: Entropy change

What does ΔG < 0 mean?

Reaction is spontaneous

What does ΔG > 0 mean?

Reaction is nonspontaneous

Endothermic

• Heat is absorbed and enters the substance. The substance is cooler than the enviornment

• ΔH > 0

Exothermic

• Heat exits to be absorbed by something else. Substance is hotter than the environment

• ΔH < 0

What’s the formula for ΔH°rxn?

ΔH_rxn∘​=∑ΔHf_products∘​−∑ΔHf_reactants∘​

Whats the formula for ΔG° (Gibbs free energy under standard conditions)?

ΔG° = -RTlnK

R: Gas constant

K: Equilibrium constant

Alpha (a) decay

• Emits an alpha particle (4​/2He)

• Decreases the atomic number (Z) by 2

• Decreases the mass number (A) by 4

Beta-minus (B-) decay

• Emits an electron (e-)

• Increases the atomic number by 1. Turns a neutron into a proton.

• No change to mass number

Beta-plus (B+) decay

• Emits a Positron (e+)

• Decreases the atomic number by 1. Turns a proton into a neutron

• No change to mass number

What’s the formula for finding out how many half-lives have passed (n)?

n = total elapsed time/half life of the isotope

What’s the half life formula?

N = N₀ (1/2)ⁿ

N₀: Initial number of atoms

n: Number of half lives elapsed

What’s the mass defect equation?

• (Mass of however many protons + neutrons are in the particle) - total mass of the particle

• “Particle” refers neutrons (1/0n) and alpha particles (4/2He)