Analytical Chem Ch. 6

Equilibrium constant equation for chemical reaction aA + bB → cC + dD

[C]^c[D]^d/[A]^a[B]^b

Conditions for evaluating an equilibrium constant

1. concentrations of solutes should be expressed as moles / liter (M)

2. Concentration of gas should be expressed in bar

3. concentration of pure solids and liquids should be omitted because they are unity

What is the equilibrium constant equation for a reverse reaction

What is K_w?

The equilibrium constant for the reaction H₂O⇌H⁺+OH^-

What is the value of K_w?

1.0×10^-14

What is enthalpy change?

The heat absorbed or released when the reaction takes place under constant applied pressure

What is standard enthalpy change?

The heat absorbed or released when all reactants and products are in standard state

What is entropy change?

The amount of energy, at a given temperature, that is dispersed into motions of the molecules in the system

What is the equation for entropy change?

△S =

Does liquid or solid have higher entropy?

Liquids have higher entropy than the same solid material because heat is required to separate molecules that are attached to eachother in the

Do ions in aqueous solution or solid salts have higher entropy?

What is △S^o?

The change in entropy (entropy of products - entropy of reactants) when all species are in their standard states

What does a positive △S^o value indicate?

That the products have more entropy than the reactants

What conditions always drive a chemical reaction toward formation of products?

Negative △H value, positive △S value

What if △S and △H have the same sign? Which direction does the reaction favor?

What is the equation for free energy?

K = e^-△Go/RT

When is a reaction spontaneous?

When △G^o is negative or if K > 1

What is Le Chatelier’s principle?

Considering a reversible reaction at equilibrium which is subjected to a change that disturbs the system, the direction in which the reaction proceeds back to equilibrium is such that the change is partially offset

What is the reaction quotient Q?

A constant that can be at any point, not strictly at equilibrium

What is the reaction quotient Q?

For a reaction at any point, [C]^c[D]^d/[A]^a[B]^b (same as K)

When is the reaction in equilibrium in terms of the reaction constants?

When K=Q

When does the equilibrium constant of an endothermic reaction increase?

When temperature increases

What is the solubility product?

The equilibrium constant in which a solid salt dissolves to give its constituent ions in solution

What is the equation of the solubility product K_sp?

K_sp= [C]^c[D]^d/[A]^a[B]^b

What is a saturated solution

A solution containing excess undissolved solid

What is the physical meaning of the solubility product?

If an aqueous solution is left in contact with excess solid salt, the salt will dissolve until the concentration of the ions in solution is equal to K_sp. After that, the amount of undissolved solid remains constant

What happens if extra ions are added to a salt solution

What is the solubility product usually used for?

To find the concentration of one ion when the concentration of another ion is fixed

What is the common ion effect?

For the ionic solubility reaction AB ⇌A⁺ + B^-,

How can precipitation be sometimes used to separate ions from eachother?

If there are two different ions in a solution, and they form salts when a third ion is added, the less soluble salt can be precipitated out to lower the concentration of the ion which reacted to make the salt

When can’t precipitation be used to separate ions?

When one substance coprecipitates with another

What is coprecipitation?

A substance whose solubility is not exceeded precipitates along with another substance whose solubility is exceeded

How does coprecipitation occur?

What is complex formation?

Increased solubility of an ion occurring as a result of the formation of

What is a ligand?

Any atom or group of atoms attached to a species of interest

What is a Lewis acid?

Accepts a pair of electrons from a Lewis base

What is a Lewis base?

Donates a pair of electrons to a Lewis acid?

What is an adduct?

The product of the reaction between a Lewis acid and a Lewis base

What is a dative or coordinate covalent bond?

The bond between a Lewis acid and Lewis base