Module 3 - Periodic Table And Energy Flashcards
Ionisation energy definition
Measures how easily an atom loses electrons to form positive ions
First ionisation energy
The energy required to remove one electron from each atom in one mole of gaseous atoms of an element to form one mole of gaseous 1+ ions.
Factors affecting ionisation energy
- atomic radius
- nuclear charge
- electron shielding
Why does atomic radius affect the ionisation energy
The greater the distance between the nucleus and the outer electrons, the less the nuclear attraction. The force of attraction falls off sharply with increasing distance, so atomic radius has a large effect
How does nuclear charge affect ionisation energy
The more protons there are in the nucleus of an atom, the greater the attraction between the nucleus and the outer electrons
How does electron shielding affect ionisation energy
Electrons are negatively charged and so inner-shell electrons repel outer-shell electrons. This repulsion, called the shielding effect, reduces the attract between the nucleus and the outer electrons
Second ionisation energy
The energy required to remove one electron from each atom in one mole of gaseous 1+ ions of an element to form one mole of gaseous 2+ ions
Metallic bonding
The strong electrostatic attraction between cations and delocalised electrons
Properties of metals
High electrical conductivity
High melting and boiling points
Not soluble
Properties of giant covalent structures
High mtp and btp as strong covalent bonds present
Insoluble in almost all solvents
Non-conductors of electricity ( only exceptions being graphene and graphite)
Why does carbon (diamond) and silicone conduct electricity
All 4 outer-shell electrons are involved in covalent bonding, so non available for conducting electricity
Why can graphene and graphite conduct electricity
Only 3 of the 4 outer-shell electrons are used in covalent bonding. The remaining electrons are released into a pool of delocalised electrons shared by all atoms in the structure
Metal + acid —>
Salt + hydrogen
Reactions of group 2 compounds with water
Hydroxide ions are released forming alkaline solutions of the metal hydroxide. When the solution is saturated any further metal and hydroxide ions will form a solid precipitate
Solubility of hydroxides with group 2 compounds
The solubility of the hydroxides in water increases down the group resulting solutions contain more OH- and are more alkaline
How are group 2 compounds used in agriculture
Ca(OH)2 is added to fields as lime by farmers to increase the Ph of acidic soils . The calcium hydroxide neutralises acid in the soil forming neutral water
Reaction colour of I2 in cyclohexane compared to water
Water = brown
Cyclohexane = violet
Reaction colour of br2 in cyclohexane and water
Water = orange
Cyclohexane = orange
Reaction colour of cl2 in cyclohexane and water
Water = pale green
Cyclohexane = pale green
Reaction between I- and cl2 and br2
I- displaces cl2 and Br p2 forming i2 so a violet layer forms
Reactions between br- and cl2 and I2
Br- displaces cl2 and forms br2 meaning mixture turns orange
No reaction takes place between Br- and i2
Reactivity trend down group 7
Atomic radius increases, more inner shells so shielding increases
Less nuclear attraction to capture an electron from another species
So reactivity decreases
What’s a disproportionating reaction
A redox reaction in which the same element is both oxidised and reduced
benefits and risks of chlorine
ensures water is fit to drink and bacteria is killed but chlorine is extremely toxic gas
carbonate test
carbonates react with acids to form co2. so
add HNO3 and bubble should form. now run the bubbles through Ca(OH)2 , a white precipitate forms if CO2 is present which turns lime water cloudy
sulphate test
add barium nitrate or barium chloride to solution (use barium nitrate if your going to do halide test after) and a white preciptate will form if sulphate is present
halide test
add aqueous silver nitrate.
chloride= white precipitate
bromide= cream precipitate
iodide= yellow precipitate
now add NH3 to check chlorine will disolve in dilute and bromine will dissolve in con NH3 but iodide wont dissolve at all
correct order when carrying out testing for ions tests
carbonate test
sulphate test
halide tests
testing for ammonium ions
add aq NaOH, mixture is warmed and ammonia ions released , lay moist indicator paper and if ammonia present paper will turn blue
whats enthalpy
a measure of the heat energy in a chemical system . enthalpy cannot be measured but enthaply changes can
enthalpy change equation
delta H = products - reactants
where does heat move in endo and exo reactions
exo- from the system to surroundings
endo- from the surroundings to the system
activation energy
the minimum energy required for a reaction to take place
standard conditions in enthalpy
pressure- 100kpa or 101kpa or 1atm
temp- 298k or 25c
conc- 1 moldm-3
in standard states
enthalpy change of reaction
the enthalpy change that accompanies a reaction in the molar quantities shown in a chemical equation under standard states and conditions
enthalpy change of formation
the enthalpy change that takes place when one mole of a compound is formed from its elements under standard states and conditions
enthalpy of combustion
the enthalpy change that takes place when 1 mole of a substance is completely reacted with o2 under standard states and conditions
enthalpy of neutralisation
the energy change that accompanies the reaction of an acid by a base to form 1 mole of H2O under standard states and conditions.
always -57Kj mol-1
specific heat capacity
the energy required to raise the temperature of 1g of a substance by 1k.
for water its 4.18 g-1 K-1
heat energy equation (Q)
q= m x c x temp change
why is the experimental values for standard enthalpy of combustion not accurate
- heat loss to the surroundings
- incomplete combustion
- evaporation of alcohol from burner wick
(all 3 lead to values being less exothermic)
-non- standard conditions
whats average bond enthalpy
the energy required to break 1 mole of a specified type of bond in a gaseous molecule .
always have positive enthalpy values
always endothermic
energy is required to break bonds
is energy released when bonds form endo or exo
exo
standard enthalpy of reaction equation
sum of reactant bond enthalpies - sum of products bond enthalpies
what does hess’ law state
if a reaction can take place by 2 routes and the starting and finishing conditions are the same the total enthalpy change must also be the same
what is meant by rate of reaction + equation for rate
measures how fast a reactant is being used up or how fast a product is being formed .
rate = change in conc/ time . units mol dm-3 S-1
things that alter the rate of reaction
conc
temp
catalyst
surface area
how does an increase in conc increase rate of reaction
as it increases the number of particles in the same volume
the particles are closer together and collide more frequently . so in the same period of time there will be more effective/successful collisions
whats a homogenous catalyst
it has the same physical state as the reactants. the catalyst reacts with the reactants and forms and intermediate. the intermediate then breaks down to give the product and regenerates the catalyst
heterogeneous catalysts
has a different state to the reactants . reactant molecules are absorbed onto the surface of the catalysts where the reaction takes place . after the reaction the product molecules leave the surface of the catalyst by desorption
whats the y axis on the boltzmann curve
number of particles with a given energy
whats the x axis on the boltzmann curve
energy
effect of temperature on the boltzmann distribution
at higher temp more molecules have an energy greater than the activation energy therefore a greater proportion of collisions will lead to a reaction .
at higher temp the actual curve is lower and shifted to the right
what does a catalyst provide
an alternate route with a lower activation energy where more particles can react successfully
in a dynamic equilibrium system..
the rate of the forwards and backwards reaction is the same
the conc of reactants and products do not change.
both the forwards and backwards reactions are occuring at the same time
a closed system
le chateliers principle
states that when a system in equilibrium is subjected an external change the system readjusts itself to minimise the effect of that change
effects of concentration changes on the equilibrium
if there are more products formed the position of equilibrium will shift to the right
if there are more reactants formed the position of the equilibrium will shift to the left
change in the position of equilibrium due to temperature
an increase in temp shifts the equilibrium position in the endothermic direction
a decrease in temp shift the equilibrium position towards the exothermic direction
the effects of pressure on the equilibrium
increasing the pressure of the system will shift the position of equilibrium to the side with fewer moles reducing the pressure on the system
decreasing the pressure shifts the position of equi to the side with more gaseous moles
kc equation
kc = prod/ react
what does kc value tell us
indicates the relative proportions of reactants and products in the equilibrium system
what does a kc value of 1 tell us
indicates the position of equilibrium that is halfway between reactants and products
what does a kc value of over 1 tell us
indicates a position of equilibrium that is towards the products
what does a kc value of less than 1 tell us
indicates a position of equilibrium that is towards the reactants
