AS physical + tests Flashcards
Test for ammonium
- Add Warm NaOH
- heat gently
- place damp red litmus above
Result - red litmus turns blue
Test for carbonates
- Add diluted HCl (aq)
- Collect gas produced
- bubble through limewater
Result - limewater goes milky
Test for sulphate
- Add barium nitrate
Result - form white p.p.
Test for halides
Add silver nitrate
Result :
Chlorine - white p.p.
Bromine - cream p.p.
Iodine - yellow p.p.
How to identify the halide test result better
Add diluted ammonia sol. to the p.p.
Chlorine - dissolve in dil. NH3
Bromine - dissolve in conc. NH3
Iodine - remains insoluble
enthalpy change
the change in heat content of a system during a reaction
enthalpy change of combustion
the enthalpy change when 1 mole of a subtance is completely combusted
enthaply change of formation
the enthalpy change when 1 mol of a compound is formed from its element
enthalpy change of neutralisation
the enthalpy change when 1 mol of water is formed from a neutralisation reaction
Activation energy
the minimum energy required for a reaction to take place
Average bond enthalpy
the energy required to break 1 mol of GASEOUS bonds
Endothermic
E(Bonds breaking) > E(bond making)
takes in energy from surrounding
Exothermic
E(Bond breaking) < E(bond making)
releases energy to surronding
Standard conditions
100 kPa and 298K
Hess’s law
the enthalpy change of a reaction is independent of the route it takes
Bond dissociation energy
Amount of energy used to break 1 mol of specific covalent bond in gaeous state
General eq for ΔHf
enthalpy change of formation
Elements -> compound
Collision theory
the theory which states that molecules must collide with:
- sufficient energy ( energy > Ea)
- at the correct orientation
for a reaction to occur
hetrogenenous catalyst
Catalyst in a DIFFERENT state to reactant
Homogenenous catalyst
Catalyst in the SAME state to reactant
Collision frequency
no. of collision per given time
3 factors that affects rate
- Temp.
2.Conc.
3.Pressure
benefits of catalyst in economic terms
- ↓temp and Pa needed
- ↓ CO2 emission
- ↓lower fuel demand
- ↓lower economic cost
3 methods to record rates
- Volume of gas produced (/time)
- change in mass (/time)
- time for dissapearance/ colour change
What are the axises for Boltzman’s distribution?
y - no. of particles
x- the energies
What 3 factors have no effect on Boltzman’s districution? Why?
Pressure, concentration and surface area
1. It increase Frq. of successful collision
2. No effect to energies of individual molecules
3. No change to shape of curve
Effect of temperature increase to Boltzman’s curve
SHIFTS RIGHT
↑ % of molecules have energies >= Ea
Effects of Catalyst on Boltzman’s distribution
- ↓ Ea
- No affect of energies of individual molecules
- ONLY greater % of molecules with energies >= Ea
Homogeneous equilibrium
An equilibrium in which all reactants are in the same state
Dynamic equilibrium
A closed system in which
* rates of foward and reverse reaction are the same
* Conc. of reactant and product are constant
Le chatellier’s principal
When a system in dynamic eqm is subject to change, the position of eqm will shifts to oppose the change.
Factors that affects position of eqm
Temp., Pressure, Conc.
NOT catalyst as it ↓ Ea for both foward and reverse
E.g Le Chatelier principal
Q: Effect on position of Eqm when temp increases?
Shifts to endothermic
E.g Le Chatelier principal
Q: Effect on position of Eqm when pressure increases?
Shifts to side with ↓ gas moles
E.g Le Chatelier principal
Q: Effect on position of Eqm when c(Product) increases?
Shifts to favor reactant (LHS)
3 optimal conditions for haber process
N2+3H2 ⇌ 2NH3
- ↑ pressure ( less gas moles on the right)
- ↓ temp. (Foward reaction is exo.)
- ↑ c( N2 + H2) and low c(NH3)
What are the comprimise to conditions for reactions ?
Need to comprimise between
1. Rate + time consumption
2. Eqm - % yield
3. safety (↑Pa - dangerous)
4. cost (↑temp - ↑ cost for fuel)
5. ↓PA - Rates maybe too slow
Indication when Kc = 1
conc(reactant) = conc(Product)
eqm at the centre
Indication when Kc < 1
conc(reactant) > conc(Product)
eqm to LHS
Indication when Kc >1
conc(reactant) < conc(Product)
eqm to PHS
