Physical Chemistry Flashcards
Name 3 common strong acids.
HCl
HNO3
H2SO4
Name a common weak acid.
Carboxylic
Name 3 common strong bases.
NaOH
KOH
Ba(OH)2
Name a commone weak base.
NH3
How can the rate of reaction be measured?
Volume of gas produced per second (Gas seringe)
Change in colour intensity (colourimeter)
Change in pH (pH meter)
How quickly a reactant disappears (Visually)
How quickly precipitate forms (Visually)
What is the rate equation?
rate = k[A][B]
How do you determine the rate constant from the half life?
k = ln2/t0.5
Where:
k=rate constant
t0.5=half life
Define ‘Rate Determinging Step’.
The slowest step.
What is the link between the rate equation and the rate determining step?
The overall rate is governed by the slowest step.
The reactants in the slowest step are in the rate equation. Vise versa.
How do you deduce orders by looking at a concentration - time graph?
Zero - Straight line, constant rate.
First - Constant half life, t1=t2
Second - Variable half life.
What does the order tell us?
The order tells us how many there are in the rate determining step.
What doesn’t effect the half life?
Concentration
What does the Arrhenius equation represent in terms of y=mx+c ?
lnk = y
-Ea/R = gradient (m)
1/T = x
lnA = c
Haloalkanes hydrolysed by hydroxide ion gives…
Alcohols
On a Maxwell-Boltzmann distribution, what does the area under the graph represent?
The total number of particles.
The total area stays the same, regardless of any changes of temperature.
On a Maxwell-Boltzmann distribution, is the peak higher or lower when the temperature is changed?
Lower temperature = Taller peak
Higher temperature = Lower peak
Reason is due to collision rate.
What are the factors that affect rate or reaction?
Concentration Surface area Pressure Temperature Catalyst
How and why does concentration affect the rate of reaction?
The higher the temperature, the faster the reaction (unless zero order).
This is because the particles are closer together so there are more frequent successful collisions.
This also applies the same way to pressure.
How and why does temperature affect the rate of reaction?
The higher the temperature, the faster the reaction.
This is because the particles have more energy and can collide more frequently, therefore there are more successful collisions.
How does a catalyst affect the rate of reaction?
A catalyst increases the rate of reaction but isn’t used up.
It lowers the activation energy meaning that a greater proportion of the collisions are successful.
How can a graph be used to find the rate of reaction?
Draw a tangent at a point, crossing both axis.
The gradient at any time represents the rate of reaction at that time.
The steeper the line, the faster the reaction.
Define redox reaction.
When one or more elements changes oxidation state.
What is a disproportionation reaction?
A reaction in which an element is both oxidised and reduced.
What is an oxidising agent?
A chemical species that removes electrons from another species.
What is a reducing agent?
A chemical species that donates electons to another species.
Define spectator ion.
An ion that exsists as a reactant and as a product in a chemican equation.
Define an acid.
Define a base.
An acid is a proton donor.
A base is a proton acceptor.
What is an alkali?
A soluble base which releases hydroxide ions into water.
Define anhydrous.
A sustance containing no water.
Define hydrated.
A chemical with water.
Define a salt.
Formed when an acid replaces H+ ions with metal or other positive ions.
What is the acid/base reaction?
Acid + Base —–> Salt + Water
What is the acid/metal reaction?
Acid + Metal —–> Salt + Hydrogen
What is the acid/carbonate reaction?
Acid + Carbonate —–> Salt + Water + Carbon Dioxide
What is a monoprotic acid? Give 3 examples.
An acid that releases one H+ ion per molecule.
eg.
HCl
HNO3
CH3COOH
What is a diprotic acid? Give 2 examples.
An acid that releases two H+ ions per molecule.
eg.
H2SO4
H2C2O4
When finding its pH, the conc needs to be x2
What is the ionic product of water (Kw) equation?
Kw = [H+][OH-]
What is the effect of temperature on the pH and neutrality of water?
As the temperature increases, equilibrium moves right to oppose the increase in temperature.
[H+] and [OH-] increase.
Therefore Kw and pH increases.
However the water is still neutral as [H+] = [OH-] (and that’s the definition of neutral)
What is the difference between a strong and a weak acid?
Strong acids completely dissociate.
Weak acids partially dissociate.
What is the colour change of phenolphthalein?
Acid —–> Alkali
Colourless —–> Pink
pH range: 8.2-10.0
What is the colour change of methyl orange?
Acid —–> Alkali
Red —–> Yellow
pH range: 3.2-4.4
On a pH curve, what does a sharp drop represent?
The range of indicators that can be used.
Which type of pH curve has no suitable indicators?
Weak acid - Weak base
What is a buffet solution?
A solution that resists changes in pH when small amounts of acid or alkali are added.
Define enthalpy change of formation.
Enthalpy change when one mole of a substance is formed from its elements with all substances in their standard states. (under standard conditions)
Define enthalpy of combustion.
Enthalpy change when one mole of a substance undergoes complete combustion in oxygen with all substances in standard states.
Define enthalpy change of neutralisation.
Enthalpy change when one mole of water is formed in a reaction between an acid and an alkali under standard conditions.
Define ionisation enthalpy.
First ionisation energy = enthalpy change when each atom in one mole of gaseous atoms loses one electron to form one mole of gaseous 1+ ions.
Second ionisation energy = the same but gaseous 1+ ions loses one electron to form one mole of gaseous 2+ ions.
Define electron affinity.
First electron affinity = enthalpy change when each atom in one mole of gaseous atoms gains one electron to form one mole of gaseous 1- ions.
Second electron affinity = the same but gaseous 1- gains an electron to formone mole of gaseous 2+ ions.
Define enthalpy of atomisation.
Enthalpy change when one mole of gaseous atoms is produced from an element in its standard state.
Define hydration enthalpy.
Enthalpy change when one mole of gaseous ions becomes hydrated (dissolved in water)
Define enthalpy change of solution.
Enthalpy change when one mole of an ionic solid (substsnce) dissolves in enough water to infinitely dilute solution.
Define bond dissociation enthalpy.
Enthalpy change when one mole of covalent bonds is broken in the gaseous state.
Define lattice enthalpy of formation.
Enthalpy change when one mole of a solid ionic substance is formed from its gaseous ions. (Under standard conditions)
Define lattice enthalpy of dissociation.
Enthalpy change when one mole of a solid ionic compound is broken up into its constituent ions in the gas phase.
