QCAA chemistry

reversible reaction

a chemical reaction in which the products re-form the original reactants

Atomic level

No change except structure, rearranged, not created or destroyed

activation energy

the minimum amount of energy required to start a chemical reaction

temperature increase in an exothermic equilibrium will cause the reaction to shift _____

left, favouring the endothermic reaction.

Temperature decrease in an exothermic equilibrium will cause a shift ___.

right, favouring the exothermic reaction.

Temperature increase in an endothermic equilibrium will see a shift ____.

right, favouring the endothermic reaction.

Temperature decrease in an endothermic reaction will see a shift ____.

left, favouring the exothermic reaction.

If pressure is increased in a system, which way will the equilibrium shift to minimise the disruption?

To the side with less molecules present.

If pressure is decreased in a equilibrium, which way will the reaction shift to minimise the disruption?

To the side with more molecules present.

How can you tell if a system is at equilibrium (graph)?

The products/ reactants will have parallel lines to one another and unchanging.

If the concentration of the reactants is increased, how will the system move to minimise the disruption?

Shift to the right - create more products.

If the products from an equilibrium are removed, what will the system do to minimise the disruption?

Shift right. There will be an effort to create more products.

Le Chatelier's Principle

States that if a stress is applied to a system at equilibrium, the system shifts in the direction that relieves the stress.

Kc =

[products]/[reactants]

Kc tells us

Indicates the relationship between product and reactant concentrations at equilibrium.

Kc <1

at equilibrium, the reactants will be favoured

Kc > 1

at equilibrium, the products will be favoured

At equilibrium Kc=

Qc

If Qc is larger than Kc, what way will the equilibrium shift to balance?

left, create more reactants.

If Qc is smaller than Kc, what way will the equilibrium shift to balance?

right, to create more products.

Acids are

proton (H+) donors

Bases are

proton acceptors

monoprotic acid

an acid that can donate only one proton (hydrogen ion) per molecule

diprotic acid

an acid that can donate two protons per molecule

polyprotic acid

an acid that can donate more than one proton per molecule

Ka =

[H+][A-]/[HA]

Kw =

[H+][OH-]

Kb =

[BH+][OH-]/[B]

Ka tells us

The dissociation of acid

pH =

-log[H+]

pOH =

-log[OH-]

Bronsted-Lowry

Common definition of acids as proton donors and bases as proton acceptors.

conjugate base

the particle that remains when an acid has donated a hydrogen ion

conjugate acid

the particle formed when a base gains a hydrogen ion

Amphiprotic

having characteristics of both an acid and a base and capable of reacting as either

buffer solution

a solution made from a weak acid and its conjugate base that neutralizes small amounts of acids or bases added to it

end point of titration

the point at which the indicator changes colour

equivalence point

the point at which the two solutions used in a titration are present in chemically equivalent amounts

half-way equivalence point

pH=pKa

titration curve

a graph of the pH of a solution as a function of the volume of the added titrant

weak acid

an acid that is only slightly ionized in aqueous solution

acid-base indicator

a chemical dye whose colour is affected by acidic and basic solutions

indicators will change colour when:

pH = pKa (choose accordingly)

REDOX reactions include:

displacement reaction of metals, combustion, explosion and electrochemical processes

redox reaction

A chemical reaction involving the transfer of one or more electrons from one reactant to another; also called oxidation-reduction reaction.

The position of an atom on the periodic table can help predict whether it will ____

be oxidised or reduced

reducing agent

The electron donor in a redox reaction, gets oxidised.

oxidisng agent

The electron acceptor in a redox reaction, gets reduced.

Oxidation

loss of electrons

reduction

gain of electrons

How to balance redox reactions in acidic conditions?

find half equations, balance all except H and O, add H+ to even the hydrogen, add H2O to balance the Os, add e- to balance charges, add half equations back together.

Oxidation number of hydrogen in a METAL HYDRIDE (NaH, CaH₂)

-1

oxidation state of transition metals can be represented by

roman numerals.

Oxidation number of oxygen in a compound with fluorine

Positive, usually +2, work it out.

Oxidation number of oxygen in peroxides

-1.E.g H₂O₂, BaO₂

Oxidation Numbers of halogens

Always -1 for fluorine and always -1 for others except when bonded to oxygen or another G17 element above them.

Which element should receive the negative oxidation number?

The most electronegative because it attracts electrons more strongly.

galvanic cell

a device in which chemical energy is changed to electrical energy

electrolytic cell

an electrochemical cell used to cause a chemical change through the application of electrical energy

reactions in a galvanic cell are _____

spontaneous

Reactions in an electrochemical cell are _____

non-spontaneous

Why is a salt bridge necessary in a galvanic cell?

Movement of charged ions

Why is an external wire necessary?

Movement of electrons

Standard electrode potential

The voltage measured under standard conditions when a half cell is connected to a standard hydrogen electrode.

oxidising and reducing agents further apart on the reactivity series of metals will have _______

higher electrode potentials

oxidising and reducing agents closer on the reactivity series of metals will have ____

lower electrode potentials

Metal plating can be completed through the use of a ______

electrolytic cell

Alkane

a hydrocarbon containing only single covalent bonds

Alkene

C=C

Alkyne

triple bond

Alcohol

R-OH

Aldehyde

CHO

Ketone

RCOR

carboxylic acid

COOH

Haloalkane

R-X (X=F, Cl, Br, I)

Ester

RCOOR

Nitrile

RCN

Amine

NH2

Amide

RC(=O)NR′R″

Stereoisomers

Compounds with the same structural formula but with a different arrangement of the atoms in space.

Structural Isomers

Compounds with the same molecular formula but different structural arrangements of the atoms within the molecule, resulting in different properties and functions.

geometric isomers

Compounds that have the same molecular formula but differ in the spatial arrangements of their atoms around a double bond. (cis and trans)

Solubility in water

whether or not a substance dissolves in water

Factors that determine solubility in water

1. polar dissolves in polar, nonpolar dissolves in nonpolar (organic)

2. compounds with less than 5 carbons and a polar group are water soluble (exception, sugars are water soluble)

3. charged functional groups are soluble in water

intermolecular forces include

dispersion forces, dipole-dipole forces, hydrogen bonds

What functional groups will form hydrogen bonds?

carboxylic acids, alcohols, amines and amides

Carboxylic acids have high boiling points as they can form...

dimers (increase the dispersion forces)

Carbonyl compounds: BP trends

higher than hydrocarbons (as O present) so dipole-dipole interactions exist

What is the general trend as hydrocarbon chain length increases?

As chain length increases, the boiling point increases. So, harder to break bonds because more energy is required to increased surface area, hence intermolecular forces.

What is the effect of branching on boiling point?

closer molecules can fit together, meaning higher IMF (higher BP)

What is the trend around BP as alcohols go from primary --> tertiary?

Primary = high BP and Tertiary = lower BP

Which would have a higher BP. Diethyl ether or n-butanol?

n-butanol as if exhibits H-bonding

Do amines and amides have stronger IMF than alcohols?

No. N is not as electronegative as O.

As hydrocarbon chain length increases, what happens to the BP?

IMFs increase, hence, there is an increase in BP.

T or F? Even numbered carbon chains will have higher IMFs than odd chains?

True. Even numbered C chains will pack together tighter

Volatility

a measure of how readily a substance vaporises

If a molecule has high IMFs and therefore a high boiling point, would you expect this to be highly volatile?

No. Due to high IMFs it will be hard to break the bonds in the molecule - won't vaporise easily

Haloalkanes are generally what state at room temperature?

liquids

Will a haloalkane have a higher BP than its' hydrocarbon derivative?

yes, due to increases molecular mass and H-bonding.

saturated hydrocarbon

A hydrocarbon in which all the bonds between carbon atoms are single bonds