CHEM 122 Final Exam

Spontaneous Reaction Prediction

K > 1, products are favored, -ΔG, -ΔH, +ΔS, and +E°.

Collision Theory

An effective collision requires particles to collide with proper orientation and sufficient energy.

Activation Energy (Ea)

A lower activation energy means a faster reaction.

Reaction Rate for Products

Rate = \frac{\Delta[concentration]}{\Delta t}

Reaction Rate for Reactants

Rate = -\frac{\Delta[concentration]}{\Delta t}

Relative Rate Law

\frac{1}{coef} (rate of rxn) = \frac{1}{coef} (rate of rxn) = …

Rate Law

Rate = k[A]^m[B]^n

Zero Order Reaction

Occurs when n=0, having units of Ms^{-}

First Order Reaction

Occurs when n=1, having units of s^-

Second Order Reaction

Occurs when n=2, having units of M^-s^-

Overall Order of Reaction

The overall order is the sum of the exponents n and m (ex: 1+1=2, second order)

Arrhenius Equation

ln(\frac{k2}{k1})=-\frac{Ea}{R}(\frac{1}{T2}-\frac{1}{T1})

Equilibrium Expression

Keq=\frac{[C]^{c}[D]^{d}}{[A]^{a}[B]^{b}}

Equilibrium Constant Inversion

The equilibrium constant is inverted when the reaction is reversed.

Effect of Coefficients on K

Multiplying coefficients by a factor raises K to the power of that factor.

Adding Equations for K

The equilibrium constant of the new equation is the product of the two original K values.

Arrhenius Acid

A substance that increases H⁺ concentration in aqueous solution.

Arrhenius Base

A substance that increases OH⁻ concentration in aqueous solution.

Bronsted-Lowry Acid

A proton donor.

Bronsted-Lowry Base

A proton acceptor.

Equilibrium Constant in Terms of Pressure

Kp=Kc(RT)^{\Delta n}

Δn

The difference in moles of products and reactants.

Calculating Conjugate Bases

Remove one H^+, subtract 1 from charge

Calculating Conjugate Acid

Add one H^+, add 1 to charge

Amphoteric Ions

Can act as an acid or a base.

Q > K

The reaction will shift to the left, favoring reactants.

Q < K

The reaction will shift to the right, favoring products.

Stress on reaction: Increase in temperature

Shift AWAY from the heat

Stress: Increase in pressure

Shift to the side with FEWER moles of gas.

Stress: Add a catalyst

No effect on the position of equilibrium.

Stress: Decrease in temperature

Shift TOWARD the heat

Comparing Ka values

When comparing two compounds, the one with a smaller Ka value is the stronger acid.

Equilibrium Expression for Ionization of Water

Kw=[OH^{-}][H_3O^{+}]

Value of Ion Product Constant Kw

1.0 x 10^{-14}

pH > 7

Basic solution

pH = 7

Neutral solution

pH < 7

Acidic solution

Calculating the pH of a strong acid

pH=-log[H_3O^{+}]

Calculating [H₃O⁺] when given pH

[H₃O⁺] = 10^-pH

Calculating the pH of a strong base

pOH = -log[OH^-]

Calculating Ka

pKa=-log(Ka)

Calculating pH or pOH

14 = pH + pOH

ICE balanced equation for weak acid

HA + H₂O ⇌ H₃O⁺ + A⁻

Can I assume x is small?

\frac{[_{}concentration]i}{Ka}>400

ICE balanced equation for weak base

A^- + H₂O ⇌ HA + OH⁻

Binary Acids

Acid strength increases across a period and down a group.

Oxyacids

More oxygens = more acidic and the more EN central atom = more acidic.

Ka-Kb Relationship

Kw = Ka x Kb

Lewis Acid

Electron pair acceptor

Lewis Base

Electron pair donor

Balanced equation for a buffer

OH^- + HA ⇌ A^- + H₂O

Henderson–Hasselbalch Equation

pH=pKa+\log\left(\frac{\left\lbrack A^{-}\right\rbrack}{\left\lbrack HA\right\rbrack}\right)

Can I use H-H equation?

[HA] and [A^-] > 0.010 M

pKa > 2.5

Bigger Ksp Value

Indicates a more soluble salt in solution.

What is the solubility product?

The equilibrium constant for the dissolution of a sparingly soluble salt which quantifies the maximum concentration of its ions in solution (Ksp)

What is molar solubility?

The number of moles of a solute that can dissolve in a liter of solution at equilibrium. (S in M)

Common Ion Effect

If a compound thrown into a solution that already has one of its ions less of the compound will dissolve.

Spontaneous Reaction

A reaction that proceeds in the forward direction without a continuous input of energy.

What is Entropy?

A measure of the disorder or randomness in a system, often associated with the amount of energy unavailable to do work. (S in J/mol·K)

High Entropy

Indicates a system with high disorder.

Low Entropy

Indicatesa system with low disorder.

Change in Entropy

\Delta S=Sf-Si

Positive Entropy Conditions (+\Delta S )

s→l→g and increase in moles of gas.

Negative Entropy Conditions (-\Delta S )

Decrease in moles of gas.

Gibbs Free Energy (Standard)

\Delta G=\Delta H-T\Delta S

Free Energy Equation (Nonstandard)

\Delta G=\Delta G\degree+RT\ln Q

Gibbs Free Energy and the Equilibrium Constant

\Delta G\degree=-RT\ln K

Voltaic Cells

Use a spontaneous reaction and generate electricity.E

Electrolytic Cells

Use energy or electricity from an external source to drive a non-spontaneous reaction.

The presence of HA and A^- being left after a reaction

Indicates a buffer solution.

Electrochemical Gibbs Free Energy

\Delta G=-nFE or \Delta G\degree=-nFE\degree

When is the Nernst equation needed?

When given concentrations that are not 1 M.