Advanced Higher Chemistry - Unit 1 - Equilibrium and Inorganic Chemistry

What does a high value of K indicate?

Higher than one, products are favoured.

What does a low value of K indicate?

Less then one, the reactants are favoured.

Does the equilibrium constant have units?

No.

Describe solids in terms of the equilibrium expression.

Solids don't have a concentration. Any solids that are present in an equilibrium equation are not included in the equilibrium equation; they are assumed to be constant and assigned the value of 1.

Describe heterogenous equilibria.

Pure liquids are considered as solvents and as such their concentration does not alter and so they are not included in the equilibrium expression; liquids are assigned the value of 1.

What is the only factor that affects the equilibrium constant.

Temperature.

What is the difference between an alkali and base.

An alkali is a soluble base.

Describe the difference between a strong and weak acid.

HCL is a strong acid because it is fully dissociated and all hydrogen ions are available. Ethanoic acid is weaker because it is only partially dissociated.

What is an acid?

A substance that is capable of donating protons.

What is a base?

A substance that is capable of accepting protons.

What is a term used to describe water?

Amphoteric (can react as an acid and a base).

Give examples of weak acids.

Ethanoic acid, carbonic acid and sulfurous acid.

Give examples of strong bases.

Metal hydroxides.

Give examples of weak bases.

Ammonia and amines.

What is a buffer solution?

Resists changes to its pH when small volumes of acid or alkali are added to it. Buffer solutions have a fixed pH.

What is a salt?

When the H+ ions of an acid are replaced by metal (or ammonium) ions.

What is an acidic buffer?

Made by mixing a weak acid and it's salt from a strong base. E.g. Ethanoic acid/sodium ethanoate.

What is a basic buffer?

Is made by mixing a weak base and it's salt from a strong acid. E.g. ammonia/ammonium chloride.

Describe how an acid buffer works.

The weak acid provides hydrogen ions; these are removed by the addition of a small volume of base. The salt of the weak acid provides the conjugate base, which can absorb excess hydrogen ions produced by the addition of a small volume of acid.

Describe how a basic buffer works.

The weak base removes excess hydrogen ions, and the conjugate acid provided by the salt supplies hydrogen ions when these are removed.

What is an indicator?

Weak acid for which the dissociation can be represented as: HIn (aq) + H2O ->

What is the colour of an indicator determined by?

The ration of [HIn] = [In-].

What is the theoretical point at which the colour change occurs in an indicator?

[H3O+] = K In.

What is the endpoint?

When we see a colour change.

What is the equivalence point?

When the number of H+ and OH- are completely neutralised.

What is a diprotic acid?

It can donate 2 protons (hydrogen ions) to a base.

What is ^H?

Difference in energy between reactants and products.

What does the degree sign mean?

Standard conditions.

What are standard conditions?

Temperature of 298K (25 degrees), pressure of 1 atmosphere and concentration of 1 mol l-1.

What is a spontaneous reaction?

A reaction that proceeds without continual energy input. For example - the burning of hydrogen - 2H2 + O2 -> 2H2O.

What is first law of thermodynamics?

Energy cannot be created or destroyed. Energy is conserved in all processes.

What is the standard enthalpy of formation?

The energy change when one mole of a substance is formed from its elements in their standard states. For example - H2 (g) + S (s) + 2O2 (g) -> H2SO4 (aq).

What is entropy?

A measure of how ordered/disordered something is. Systems that are highly ordered have low entropy and systems that are associated with disorder have high entropy.

Does water freezing show an increase or decrease in entropy?

Decrease.

Does NH4NO3 (s) -> N2O (s) + 2H2O (g), show an increase or decrease in entropy?

Increase.

What is the entropy of solids and gases?

Solids is low and gases is high.

What factors increase entropy?

As temperature increases, as vibrations increase, when many substances form solutions, when a mixture is formed, an increased number of moles.

When is there an increase in entropy?

There is a rapid incase in entropy at the melting point of a substance and an even more rapid and larger change in entropy at the boiling point.

What does the second law of thermodynamics state?

The total entropy of a reaction system and its surroundings always increases for a spontaneous process.

What does heat energy released by the reaction system to the surroundings do?

Increases the entropy of the surroundings.

What does heat energy absorbed by the reaction system do to the surroundings?

Decreases the entropy of the surroundings.

What is the third law of thermodynamics?

States that entropy falls to zero at absolute zero - (0K). (-273 degrees Celsius).

Describe elements in terms of enthalpy and entropy.

They don't have an enthalpy value but they have an entropy value.

What is the standard entropy of a substance?

The entropy value for the substance in its standard state.

What is a feasible reaction?

One that tends towards the products rather than the reactants. This does not give any indication of the rate of reaction.

When is a reaction more likely to be spontaneous?

If it is exothermic, but endothermic reactions can still be spontaneous. If there is an increase in disorder, but reactions that decrease disorder can still be spontaneous.

What happens if ^Go is negative?

The reaction is feasible.

What happens if ^Go is positive?

The reaction isn't spontaneous.

What happens if ^Go is zero?

The system is at equilibrium.

How do you work out the temperature at which a reaction is feasible?

T = ^H divided by ^S. Remember to divide ^S by 1000.

What happens if ^Go is less than 0?

K>1, the equilibrium mixture is mainly products.

What happens if ^Go is more than zero?

K

What happens if ^Go is equal to zero?

K=1, the equilibrium mixture contains comparable concentrations of reactants and products.

What can thermodynamics predict?

Whether a reaction is feasible or not, the conditions necessary for a reaction to be feasible and the position of equilibrium.

What is the reaction characteristic if ^H is -, ^S is + and -T^S is -.

Negative and spontaneous at all temps.

What is the reaction characteristic if ^H is +, ^S is + and -T^S is +.

Positive and non-spontaneous at all temps.

What is the reaction characteristic if ^H is -, ^S is - and -T^S is +.

Positive or negative, spontaneous at low temps.

What is the reaction characteristic if ^H is +, ^S is + and -T^S is -.

Positive or negative and spontaneous at high temp.

What is the only way to determine reaction kinetics?

By carrying out experiments in the reaction under investigation.

What can not determine the order of reaction from?

A balanced equation.

What are orders?

Numbers, usually with values of 0,1,2 or 3.

What order occurs when doubling [reactant] = double rate?

First order

What order occurs when doubling [reactant] = no effect on rate?

Zero order.

[B] x3 = rate x3. What is the order of B?

First order.

[C] x2 = rate x4. What is the order of C?

Second order.

What is the general rule for a zero order reactant?

Changing the concentration will have no effect on the reaction rate.

What is the general rule for a first order reactant?

Reaction rate changes in direct protection to concentration change.

What is the general rule for a second order reactant?

Rate changes in line with the square of the concentration.

What are the units for k[A]?

s^-1

What are the units for k[A][B]?

l mol^-1 s^-1

What are the units for k[A][B][C]?

l^2 mol^-2 s^-1

How fast is a chemical reaction?

Only as fast as it's slowest step.

What is the slowest step in a chemical reaction?

The rate determining step (R.D.S).

What does the rate of a chemical reaction depend on?

The concentrations of the reactants.

What is a reaction mechanism?

A series of steps that reactions usually occur by.

How can you measure the rate of a chemical reaction?

Sampling, Gas Evolution, Colourimeter, pH.