Chemical Reactivity

Front 1

Affect of Concentration on Reaction Rate

Back 1

Increase concentration - increase no. of particles - increase the chance and frequency of a collision - so increase the no. of successful collisions so overall increase rate of reaction. NOTE: Increasing conc. does not necessarily increase rate as many reactions occur in steps; depends on slowest step

Front 2

Affect of Temperature on Reaction Rate

Back 2

Increase temperature - increase kinetic energy of particles - increase the chance and frequency of a collision - so increase the no. of successful collisions so overall increase rate of reaction. ALSO the more energy a particle has the more likely it is to the activation energy required to be successful. Larger fraction of collisions will be successful.

Front 3

Affect of Surface Area on Reaction Rate

Back 3

Increase state of matter - increase no. of available particles - increase the chance and frequency of a collision - so increase the no. of successful collisions so overall increase rate of reaction.

Front 4

Rate of Reaction depends on...

Back 4

Frequency of collisions
Fraction of colliding molecules with sufficient energy to form a successful collision.

Front 5

Activation energy (Eact)

Back 5

Minimum amount of energy a collision must have to be successful. When colliding molecules approach very closely their e- fields repel and gain potential energy. Must have enough kinetic energy to overcome the repulsive force and surmount energy barrier. Must have Eact. Higher Eact slower rate.

Front 6

Activated Complex

Back 6

At the point of the collision the arrangement of atoms at the summit of the energy profile is called the activated complex and this high energy cluster only exists briefly.

Front 7

Catalyst

Back 7

Lowers the Eact by providing a shorter and easier reaction energy pathway. Increases ROR without undergoing any permanent chemical change or being used up.

Front 8

Equalibrium

Back 8

Reversible physical changes, e.g. when a solid dissolves and crystallises at the same time and rate so that there is no visible change. It is dynamic as there always appears to be the same amount of each substance but really the particles are moving backwards and forwards.

Front 9

Conditions of Equilibrium

Back 9

Constant temp., closed system, constant pressure (amount of gas). If any of these are altered the equilibrium is disturbed and a new equilibrium must be established as the system responds with an imposing change. Composition of the mixture is altered.

Front 10

Kc Value

Back 10

Extent of the forwards reaction.
For: aA + bB --> cC + dD
Kc = [C]c[D]d / [A]a[B]b
Right/Left
If temp. alters then Kc alters

Front 11

Kc Magnitude

Back 11

=1: approximately equal concentration on the RHS and LHS
very large: forwards reaction has almost gone to completion (RHS more concentrated)
very small: reaction has not proceeded very far (LHS more concentrated.

Front 12

Heterogenous Equilibrium

Back 12

More than two states present. The conc. of a pure solid/liquid is consistent and independent to the amount present so it must be emitted from the Kc value. The concentration of the components will always give the same Kc value at the same temp.

Front 13

Disturbing Equilibrium

Back 13

Conditions altered
Reverse Rate \\=\\ Forwards

Front 14

Effect of Concentration on Equilibrium

Back 14

If the concentration of a component of the equilibrium is altered, the system shifts to reduce the effects of the change. If the concentration is increased, the reaction that consumes that substance is favoured and the equilibrium shifts away from that substance. If the concentration of a substance is decreased, the reaction that produces that substance is favoured, and the equilibrium shifts toward that substance.

Front 15

Effect of Temperature on Equilibrium

Back 15

Increase the temp. favours the endothermic reaction as it absorbs the excess heat energy and dec. favours the exothermic as the surroundings can absorb more of the heat energy produced. This will also alter the Kc as the amount of products and reactants is altering.

Front 16

Effect of Pressure Change on Equilibrium

Back 16

Increase the pressure (only for gases) and the side with the smallest number of gaseous molecules is favoured as the equilibrium attempts to react as many gaseous molecules as possible to reduce the effect of the change to the system. If you add inert gases this increases the total pressure but does not effect equilibrium as they are independent to the mixture.

Front 17

Effect of a Catalyst on Equilibrium

Back 17

A catalyst has no effect, only increases the ROR both forwards and backwards equally. Equilibrium is reached faster.

Front 18

Acid Properties

Back 18

Sour, pH less than 7, turn litmus red
MASHO
BASHO
CASHOCO

Front 19

Basic/Alkali Properties

Back 19

Soapy, pH larger than 7, turn litmmus blue
NaOH and KOH react with a few metals (Al and Zn) to give H2 and a complex compound.
Alkali + Ammonia Salt --> Salt + H2O

Front 20

Hydronium Ion

Back 20

Due to its small size and +ve charge H+ cannot exist by itself in solution. Becomes attached to a water molecule forming a dative bond producing the hydronium ion H3O+.

Front 21

Dissociation of water - An equilibrium reaction

Back 21

2Water >--< OH- + H3O+
Hardly proceeds right (does not readily dissociate) as:
Kw = [H3O+][OH-] = 1x10-14 (at 25 degrees celsius)
If a substance is added which donate H+ [H3O+] inc. so [OH-} must decrease and the opposite occurs if something is added which accepts protons.

Front 22

In an acidic solution and in a basic solution [OH-], [H3O+] and 1x10-7 are...

Back 22

Acidic: [H3O+] > [OH-] > 1x10-7 mol/L
Basic: [H3O+] < [OH-] < 1x10-7 mol/L
NOTE: To Calc either [OH-] or [H3O+] rearrange
[OH-][H3O+] = 1x10-14

Front 23

pH scale

Back 23

Acidic: [H3O+] > 1x10-7 and Basic: [H3O+] < 1x10-7
Measured by: pH = -log[H3O+] or UI (ROYGBIV)
pH is a measure of the concentration of H3O+ ions in the products.

Front 24

Strong Acids

Back 24

Completely dissociate in solution. Only exist as ions and not molecules.
H2O + HCl --> H3O+ + Cl-

Front 25

Weak Acids

Back 25

Partially dissociate in solution and exist at equilibrium.
e.g. CH3COOH + H2O >--< H3O+ + CH3COO-
Large number of molecules and fewer ions so large Ka value.
Cannot calculate pH

Front 26

Strong Alkalis

Back 26

Completely dissociate in solution. Only exist as ions and not molecules.
NaOH --> Na+ + OH-
If given [OH-]: pOH = -log[OH-] or pH = 14 - (-log[OH-])

Front 27

Weak Alkalis

Back 27

Partially dissociate in solution and exist at equilibrium.
e.g. NH3 + H2O >--< OH- + NH4+
Large number of molecules and fewer ions so large Kb value.
Cannot calculate pH

Front 28

Conduction of weak vs strong bases and acids

Back 28

To conduct must have ions free to carry the charge. Strong conducts better than weak as it completely dissociates in solution so there are more available ions to carry charge than weak with only partially dissociates and exists at equilibrium, not as many free ions, more molecules.

Front 29

ROR between weak and strong acids

Back 29

Strong acid has a faster ROR as it completely dissociates so there are more available particles to react whereas a weak acid does not and exists at equilibrium so there are fewer particles to react. e.g. when CH3COOH in solution reacts with a carbonate it will upset the equilibrium as more water is produced and so the forwards reaction is favoured. Eventually enough ions will be produced so all carbonates react, but will take a while.

Front 30

Salt

Back 30

Ionic compound, large difference in electronegativity, solid ions locked in a lattice structure, not a conductor. Reacts with water - known as hydrolysis.

Front 31

pH of salts

Back 31

Some salts when split into their ions will react with water and become slightly acidic or basic. e.g. carbonate ions react with water to become slightly basic and ammonium ions react to become slightly acidic.

Front 32

Bronsted Lowry Theory

Back 32

An acid is a substance that donates a proton and a base accepts, BAAD
Some substances are amphoteric e.g. water can both donate and accept protons (H+)

Front 33

Conjugate Acid/Bases

Back 33

Donate and accept reversibly e.g. in the dissociation of a weak acid H3O+ can donate H+ ions and reverse the reaction (conjugate base). A strong acid is a good proton donor and its conjugate base is weak (poor proton donor) so it only ever goes one way. A weak acid is the opposite so it is easy to reverse the reaction and there are more molecules than ions.