Periodic Table And Energy Flashcards
Def of qualitative analysis
Analysis that relies on observations rather than numerical values to determine results of test
Carbonate test
-what does it test for
-word equation
-positive result
- tests for carbonate ions (CO3^2-)
- Carbonates + acids —> carbon dioxide gas (+metal salt)
- gas collected will turn limewater cloudy
sulfate test
-what does it test for
-word equation
-positive result
- sulfate ions (most sulfates soluble but Barium sulfate is insoluble)
- Ba (aq) + XSO4 (aq) —> BaSO4 + X
- if solution turns into white precipitate
Halides test
-what does it test for
-ionic equation
-positive result
-halides (most halides soluble but silver halides are insoluble)
- Ag+(aq) + Cl- (aq) —> AgCl (s)
Def first ionising energy
The energy required to remove one electron for each atom in one mole of gaseous atoms
How does 1st ionisation energy change down groups?
+why
Down the groups it decreases
-increased shielding from inner electrons (repelling outer)
- increased distance from the nucleus (weaker attraction)
- increase in nuclear charge (no effects as the others are more effective)
Trend of 1st ionisation energy across period ?
+why
General increase across period
As ^nuclear charge, no change of shielding/ distance
But
- small drop between group 2/3 as P subshell (further way) used not S
- slight drop between group 5/6 as paring electrons in P subshell (increases repulsion)
Def of metallic bonds?
Strong electrostatic attraction between cations (+) and delocalised electrons
Cations= fixed position
Delocalised electrons = mobile
Names of groups
1) alkaline metals
2) alkaline earth metals
3-12) transition metals
15) pnictogens
16) chalogens
17) halogens
18) noble gases
Equation for 1st ionisation energy
X (g) —> X+ (g) + e-
Sketch a graph to show 1st ionisation energy across periodic table
See notes
Trends of bonding across Period 3
Giant metallic (Na, Mg, Al)
Giant covalent (Si)
Simple molecular (P,S,Cl)
Simple atomic (Ar)
Factors that strengthen metallic bond (higher melting point)
More charge dense (E.g Al3+ not Na+)
More delocalised electrons involved in the bonding
Trend of reactivity down group 2 +why?
Reactivity increases
Ionisation energy decreases due to increase separation and shielding of electrons
Soluble compounds
Group 2
Group 2 chlorides
Group 2 sulphate get progressively less soluble
Group 2 hydroxides become more soluble down group
All nitrates
Reaction of Mg
1) oxygen
2) water
3) acid
Mg - silver solid
1) bright white flame leaving white solid
2) very slowly fizzes, UI turns greens/blue, colourless gas and solution
3) fizzes vigorously colourless gas and solution
Reaction of Ca
1) oxygen
2) water
3) acid
Ca- silver solid
1) vigorously with red flame leaving white solid
2) fizzes vigorously, produces white solid, UI - purple
3) fizzes vigorously, colourless flammable gas released, colourless solution
Reaction of Sr
1) oxygen
2) water
3) acid
Sr- silver solid
1) very vigorously with red flame leaving white solid
2) fizzes vigorously, produces white solid, UI - purple
3) fizzes vigorously, colourless flammable gas released, colourless solution
Reaction of Ba
1) oxygen
2) water
3) acid
Ba- dark grey silver solid
1) very vigorously with green flame leaving white solid
2) fizzes vigorously, produces white solid, UI - purple
3) fizzes vigorously, colourless flammable gas released, colourless solution
Trend of boiling/ melting points down halogen (group 7)?
+ describe
Boiling/ melting point increases down the group
Due to ;
More e- means more induced dipole-dipole (LONDON FORCES) so more energy required to separate the molecules
Trend of reactivity in Halogens
- illustrate example with reaction with other halide ions
Reactivity decrease down the group
Cl2 (aq) [GREEN] + 2Br- (aq) —> Br2 (aq) [ORANGE] + 2 Cl- (aq)
Cl2 (aq) [GREEN] + 2I - (aq) —> I2 (aq) [ PURPLE] + 2Cl- (aq)
Br2 (aq) [ORANGE] + 2I - (aq) —> I2 (aq) [ PURPLE] + 2Br- (aq)
Benefits ans risks of using chlorine in water treatment?
BENEFITS
- cheap & effective so less economically developed countries can use it
- kills bacteria ensure water is safe to drink
RISKS
- more economically developed countries us UV/ozone as can justify increased costs due to concerns around Cl2
- chlorinated hydrocarbons can be carcinogenic
substance used to test for different halide ions? + the general reaction
Aqueous silver ions
Ag + (aq)
Reaction:
Ag+ (aq) + X- (aq) —> AgX (s)
Results of the test for different halides?
Aqueous silver ions added:
AgF = no precipitate formed
AgCl = white solid that is soluble in dilute& concentrated ammonia (NH3)
AgBr = cream solid that is soluble in concentrate ammonia (NH3)
AgI = yellow solid that is insoluble in dilute & concentrated ammonia (NH3)
Why ammonia is added after halide test?
To confirm results when the colours could be ambiguous
Reaction that occurs:
AgX(s) + 2NH3 (aq) —> [Aq(NH3)2] (s) + X- (aq)
Where’s X is Br or Cl not I
Reaction of chlorine with water in purification? + what type of reaction is this
Cl2 + H2O —> HClO + HCl
HClO dissolves to form ClO- (chlorate (1) Ions) & HClO (hypochlorocic acid)- bleach
This is a disproportion rections as the chlorine is both oxidised from ON =0 (Cl2) to ON= +1 (HClO) as well as reduced to ON= -1 (HCl) in the same step
Reaction of Cl with aq NaOH to form bleach
Cl2 + 2 NaOH —> NaClO + NaCl + H2O
This is disproportion rections as the chlorine is both oxidised from ON =0 (Cl2) to ON= +1 (NaClO) as well as reduced to ON= -1 (NaCl) in the same step
Trend in of group 2 hydroxides?
- solubility
- pH values
- alkalinity
Mg(OH)2 is slightly soluble & lower dissociation so pH 10
Ba(OH)2 is much more soluble & higher dissociation so pH 13
Down group 2:
- solubility increases
-pH increases
- Alkalinity increases
Group 2 compounds uses in agriculture?
+ equation
Ca(OH)2 added to fields to increase pH of acidic soils as it neutralises acid in soil forming neutral water
Ca(OH)2 [s] + 2H+ [aq] —> Ca+ [aq] + 2H2O [l]
Group 2 compounds uses in medicine?
+ equation
Often uses at antacids for treating indigestion
E.g magnesium hydroxides/carbonate
Mg(OH)2 [s] + 2HCl [aq] —> MgCl2 [aq] + 2H2O [l]
Or
Calcium carbonate
CaCO3[s] + 2HCl [aq] —> CaCl [aq] + 2H2O [l] + CO2 [g]
What order do you carry out qualitative tests?
1) test for Carbonates
- using dilute nitric acid ( HNO3)
2) test for sulfates
- using barium nitrate
3) test for halogens
- using silver nitrate then ammonia
Test for ammonium ions? (NH4+)
1) add sodium hydroxide to from ammonia +water
2) release ammonia gas by heating gently
3) test for ammonia using damp litmus paper -> blue if positive
NH4+ [aq] + OH- [aq] —> NH3 [g] + H2O [l]
Describe rate of reaction graph
1) the rate is fastest at start of reaction due to highest concentration of reactants
-steepest curve
2) rate of reaction slows down as reaction proceeds as reactants are being used up.
- shallowing out
3) once reactants have been used to rate of reaction is zero
- graph plateaus
Adv/ disadv of using catalysts
adv
- speed up rate of reaction which saves money because plant doesn’t have to be open as long
- allow reactions to occur at lower temperature reducing carbon footprint
- save industries money by reducing fuel cost
- can be used repeatedly
disadv
- very expensive to buy
- need to be removed from products before reused
- different reactions use different catalysts
- catalysts can be ruined by impurities
- heavy metal extractions create toxic contamination
Difference between heterogeneous and homogeneous catalysts
Heterogeneous = catalyst in different phase from the reactant the reaction occurs on its surface. Reactant binds (absorbs) to the surface increasing likelihood of meeting and inducing stress in bonds lower AE
homogeneous = catalyst and reactant are in same phase, the reaction proceeds through an intermediate species. The catalyst is changed into a product and then that product is used and reforms the catalyst. These 2 reactions require less energy overall.
What is Boltzmann distribution?
(Graphs for reactions)
Boltzmann distribution shows the number of molecules with a given energy.
Knowing activation energy in relation to energy of particles allows you to find area under curve which= particles above Ea that will react if collide.
temperature effect on Boltzmann distribution graph
Temperature increase
1) peak moves to the right
2) peak broadens
3) peak lowers
Overall result more particles with Ea so rate of reaction increases as more successful collisions
Draw enthalpy profile diagram for
Exothermic & endothermic reaction
See notes
Exothermic - goes down in level as heat is given out
Endothermic- goes up in level as energy is taken in from surroundings
Def of activation energy
The minimum energy requires for a reaction to take place
Def of standard conditions/ standard state
The physical states under standard conditions of a chemical
E.g solid/ liquid/ gas at RTP
Def of enthalpy change
The heat energy change that occurs during a process under constant pressure
def of enthalpy change of reaction
∆rH
Enthap change asociated with a stated equation
Def enthalpy change of formation
∆fH
Enthalpy change when 1 Mol of a compound is fromed from its elements in their standard states
Def of enthapy of combuation
∆cH
Enthalpy change when 1 mole of a substance undergoes complete combustion
Def of enthalpy change of neutralisation
∆neutH
Enthalpy change when 1 mole of water is formed from 1 mole of aq H+ nad 1 mole of OH-
What are considered to be standard conditions? + how do we show this in enthalpy changes
Pressure of 100 KPa and temperature of 298 K
Plimsoll line (⦵ ) used to indicate standard conditions (it appears after the H)
Calculation of enthalpy changes using bond energies
(Sum of bonds broken) - (sum of bonds formed) = enthalpy change
If negative reaction = exothermic
If positive reaction = endothermic
(This however is an average value)
Method to directly measure energy change of a reaction
calorimetry
1) coffee cup calorimeter
- insulated polystyrene cup with measured volume of water with which reaction occurs
- temp change of water is measured using SHC of water energy change is calculated
- insulation is used around polystyrene cup to minimise heat loss to surroundings
2) Copper cup Calorimeter
- copper cup with known volume of water is heated above fuel
- same as above to calculate energy change
- fraught shields used to minimise heat loss to surroundings
Formula to Calc energy change
Q = mc ∆T
Where:
Q - energy change in J
M- mass of water/ solution in g
C- specific heat capacity of water (solution assumed pure water) = 4.18 Jg-1oC-1
∆T - change in temperature of water in oC
Formula to Calc enthalpy change from energy change
+ what happens if you have two solutions?
∆H = -q/ n
Negative energy change used (-q) - as energy the chemicals lost is what was gained bu the surrounding we measured
+if you have 2 values for moles use the lowest one s this reaction is what is limiting in the reaction
Method of compensation for heat loss by calibrating calorimetry
1) if you draw a cooling curve graph
- draw a vertical line from the time that solutions were mixed (beginning of reaction)
- draw straight diagonal line from the downwards path of graph
Were those two points meet is the max temperature reached ∆T which can the be used in calculations
[ see notes for more info]
2) if you calculate from a known reaction then you can find mc =C that can be used with you later reactions
See notes
Draw an example of Hess’ laws and enthalpy cycles (using hydrocarbon as example)
See sheet
Formula to calc enthalpy change from combustion reaction on Hess’ cycle
Formula to calcu enthalpy Change from formation reaction on Hess’ cycle
Draw out cycle
Use arrows as vectors
Formation = compound formed from elements in their standard states
explain the difference in melting points of P4 and Cl2
Phosphorus has more electrons in its bonded molecule therefore stronger/more London forces that require more energy to break than Cl2
Physical properties of giant metallic
Electrical conductivity
High melting and boiling points
Don’t dissolve (low solubility)
Physical properties of giant covalent structures
High melting points
Insoluble
Non conductive
Trends in melting points across period 2 and 3
Across period 2 & 3
- melting point increases from group 1 to group 4
- sharp decrease in melting point between group 4 and group 5
Due to change from giant to simple molecular structures - melting point comparatively low from group 5 to group 18
Giant structures have strong forces to becomes so high melting point whereas simple molecular have weaker intermolecular forces
Def of average bond enthalpy
Breaking 1 mol of bonds in gaseous molecules
Reaction of group 2 oxides with water
+general equation
+ trends in alkalinity
Group 2 oxide react with water —. Releasing OH ions forming alkaline solution
CaO(s) + H2O —> Ca2+ + 2OH-(aq)
Group 2 are weakly alkaline with elements further down having increased alkalinity
Trends in boiling point of group 7
At RTP all halogens exists as diatomic molecules (X2)
Down group 7
- more electrons
- stronger London forces
- more energy to break London forces
- boiling point … increases down group
Formula to calc enthalpy change from experiment
Q (energy) = m (mass of water/solvent) c (specific heat capacity) T (change in temp)
Enthalpy change = -Q/moles
When is dynamic equilibrium reached?
In a close system when the rate of the forward reaction is equal to the rate of the reverse reaction and the concentrations of the reactants and products do not change
