chemistry important things to remember

In an open system, what can be exchanged with the surroundings of the system?

Energy and mass

In a closed system, what can be exchanged with the surroundings of the system?

Energy

What is Le Chatelier’s principle?

If a system in equilibrium is subject to a change, the system will act to partially oppose that change.

What happens when the concentration of a species increases?

The reaction (direction) that uses this species as a reactant will be favoured.

What happens when there is an increase in pressure or a decrease in volume (if gaseous species)?

The reaction (direction) that produces the fewest moles will be favoured.

What happens when a solution is diluted or there is a decrease in concentration (if aqueous species)?

The reaction (direction) that produces the most moles will be favoured.

What happens when the temperature is increased?

The endothermic reaction (direction) will be favoured.

What happens to the equilibrium constant when there is an increase in the concentration of a species?

If a reactant is added, the equilibrium constant will decrease at the time of change, then return to the original value from before the change once it reaches equilibrium again.

What happens to the equilibrium constant when there is an increase in pressure or decrease in volume?

It will stay the same.

What happens to the equilibrium constant when a solution is diluted or when there is a decrease in concentration?

It will stay the same.

What happens to the equilibrium constant when temperature is increased?

It decreases.

What does a heterogeneous system mean?

Where not everything is in the same phase.

What does a homozygous system mean?

Where all reactants and products are in the same state.

What is the only way to change the value of the equilibrium constant of a reaction?

Changing the temperature.

When Kc < 10^-4 , what does this indicate?

There is a large amount of reactant (equilibrium sits left, indicating a negligible reaction).

When Kc > 10⁴ , what does this indicate?

There is a large amount of product (equilibrium sits right, indicating a complete reaction).

When 10^-4 < Kc < 10⁴ , what does this indicate?

There is a good amount of reactant and product (indicating a significant reaction).

What happens when Qc < Kc?

The system will continue with the forward reaction to achieve equilibrium.

What happens when Qc > Kc?

The system will continue with the reverse reaction to achieve equilibrium.

What does it mean when Qc = Kc?

The reaction is at equilibrium.

What does Ksp tell us?

A measure of the solubility of an ionic compound.

What does a higher Ksp value represent?

Higher solubility (more can dissolve before the solution becomes saturated).

What does a lower Ksp value represent?

Lower solubility (less can dissolve before the solution becomes saturated).

What does it mean when Qc < Ksp?

No precipitate formed (solution is unsaturated), you can still dissolve more of the solid ionic compound.

What does it mean when Qc = Ksp?

No precipitate formed (solution is saturated), but you can’t dissolve more of the solid ionic compound.

What does it mean when Qc > Ksp?

Precipitate will form (solution is supersaturated), but you can’t dissolve more of the solid ionic compound.

What are examples of weak acids?

Carboxylic acids and carbonic acids.

What are examples of strong acids?

Hydrochloric acid, nitric acid, and sulfuric acid.

What are examples of weak bases?

Ammonia and amines.

What are examples of strong bases?

Group 1 hydroxides (e.g. KOH) and barium hydroxide.

What is the chemical reaction for a weak acid indicator?

HIn —> H+ + In-

What is the chemical reaction for a weak base indicator?

BOH —> B+ + OH-

What is meant by the half-equivalence point in titration?

When pH = pKa.

What is meant by the buffer region in titration?

The section between the initial point and the equivalence point.

Where do electrons travel in an electrolytic cell?

From the cathode (which is positive in electrolytic cells) to the anode (which is positive).

Where do electrons travel in a galvanic cell?

From the anode to the cathode.

What is the product that is produced by fuel cells?

Water

For a hydrogen fuel cell under acidic conditions, what is the anode half-equation?

H2 —> 2H+ + 2e-

For a hydrogen fuel cell under acidic conditions, what is the cathode half-equation?

O2 + 4H+ + 4e- —> 2H2O

For a hydrogen fuel cell under alkaline conditions, what is the anode half-equation?

H2 + 2OH- —> 2H2O + 2e-

For a hydrogen fuel cell under alkaline conditions, what is the cathode half-equation?

O2 + 2H2O + 4e- —> 4OH-

What does it mean when a compound is saturated?

Contains only single bonds.

What does it mean when a compound is unsaturated?

Has at least one double or triple bond.

What is the difference between molecular, empirical, and structural formulas:?

Molecular represents how many of each type of atom there are in the molecule, empirical represents the lowest ratio, and structural represents the atoms in the order they appear.

What is a structural isomer?

Have the same molecular formula but different structural formulas.

What are stereoisomers?

Molecules with the same molecular formula but different spatial arrangement of atoms.

What is the difference between a cis and trans isomer?

In cis, atoms are positioned on the same side, whereas in trans, they are on different sides.

What is a chiral carbon?

A carbon that has four unique groups attached to it.

What conditions are required for the oxidation of alcohols?

An oxidising agent such as acidified permanganate ions (MnO4- and H+) or acidified dichromate ions (Cr2O7 2- and H+).

What is required when an alkane undergoes substitution to form a haloalkane?

UV light

What is required when a haloalkane undergoes substitution to produce an alcohol?

NaOH

What is required when a haloalkane undergoes substitution to produce an amine?

NH3

What is Markovnikov’s rule?

The hydrogen atom is more likely to bond with a carbon atom that has more hydrogens bound to it and the halogen is more likely to bond with a carbon atom with fewer hydrogens bound to it.

What is required in the addition reaction of an alkene to produce an alcohol?

Heat, water, and an acid catalyst.

What is required in the condensation reaction between an alcohol and a carboxylic acid to produce an ester?

Concentrated H2SO4

What is required in the condensation reaction between a carboxylic acid and an amine to produce an amide?

Heat

What is required in the reduction of alkenes to produce alkanes?

H2 and a metal catalyst (e.g. Pt).

What is required to make an alkene from a haloalkane via elimination?

A base (e.g. alcoholic KOH).

How would you distinguish between an alkane and an alkene using a chemical test?

The bromine water test, which takes advantage of the fact that the reaction of an alkane with Br2 requires UV light, whereas the reaction of an alkene with Br2 does not. If a colour change occurs it confirms an alkene as the solution will turn from orange to colourless, whereas an alkane will show no change without UV light.

What observation is important in the reaction of a carboxylic acid and an alcohol?

A fruity smell.

How would you determine the type of alcohol a substance is using a chemical test?

Use oxidising agents to see if a colour change occurs. If there is no colour change, the alcohol is tertiary. Otherwise, you will need to see if the alcohol can be oxidised again. If it can be oxidised twice, it is primary, but if it can only be oxidised once, it is secondary.