Module 3 Flashcards
define first ionisation energy
the energy needed to remove 1 mole of electrons from 1 mole of gaseous atoms
what factors effect an elements ionisation energy
atomic radius, nuclear charge, sheilding
define second ionisation energy
energy needed to remove 1 electron from each ion in one mole of gaseous 1+ ions to form 1 mole of gaseous 2+ ions.
trends in ionsiation energy across a period
increases going from left to right. Atomic radius decreases, nuclear charge increases but shielding stays the same so there are stronger electrostatic forces.
trends in ionisation energy down a group
decreases as more electron shells so increased shielding and increased atomic radius causing weaker electrostatic forces. This counteracts the increase in nuclear charge.
Trend in MP/BP across period 2 and 3.
increases from group 1-14. (stronger metallic bonds as more positive ions are formed or giant covalent structures). Sharp decrease from group 14 - 15 (change from giant to simple structures). comparatively low from 15-18.
How can you tell how many electrons an element has in its outer shell
Looking at the ionisation energies. The biggest jump in ionisation energy is where it loses an electron shell e.g. if there is the biggest jump between 4 and 5 ionisation energy then there were 4 electrons in the outer shell.
why does ionisation energy drastically increases once all the electrons in the outer shell have been removed
decrease in shielding, decrease in atomic radius and increase in effectiveness of nuclear charge.
trend in reactiveness of group 2 elements
as you go down the group it is more reactive as it is easier to lose electrons
write a general equation for the reaction of water with a group 2 metal using M to represent the metal
M(s)+ 2H2O(l) —– M(OH)2(aq) + H2(g)
write an equation to show formation of metal hydroxide from a group 2 metal oxide and water
CaO(s) + H2O(l) —– Ca(OH)2(s)
solubility of group 2 metal hydroxides trend
as you go down the group solubility/alkalinity increases
chemical formula for lime water
Ca(OH)2
what is slaked lime and what is it used for
calcium hydroxide - added to fields of lime to increase pH of acidic soils
what calcium compound is used in indigestion treatments
calcium carbonate
describe test for sulphate ions
Acidify BaCl2 by adding a few drops of HCl. Add this to the solution. If sulphate ions are present then a white precipitate of BaSO4 forms.
state the chemical name and the use for barium meal. Why can barium not be swallowed but barium meal can
barium sulfate - detects abnormalities in the esophagus, stomach and small bowel. Bariums sulfate is not toxic unlike barium.
chemical formula and use for ‘milk of magnesia’ and why it has this name.
Mg(OH)2 - treats acid indigestion. Has a milky white colour.
trend in reactivity of group 17
reactivity decreases going down the group (harder to gain an electron)
boiling point trend of group 17
increases going down the group as there are stronger london forces as there are more electrons.
what is a halide
any group 17 element that has formed an ion
ionic equation for test for halides
Ag+(aq) + X-(aq) —- AgX(s)
describe the test for halides
add aqueous silver nitrate to aqueous solution. If halide present precipitate forms. Add aqueous ammonia to test solubility of precipitate
colour of precipitate and solubility of Cl in NH3
white. Soluble in dilute NH3
colour of precipitate and solubility of Br in NH3
cream. Soluble in concentrated NH3
colour of precipitate and solubility of I in NH3
yellow. Insoluble in concentrated NH3
ionic equation for carbonate test
2H+(aq) +CO3(2-)(aq) —— CO2(g) + H2O(l)
describe the carbonate test
add dilute nitric acid to solution. If you see bubbles it could be carbonate. Bubble gas through lime water if it turns cloudy then carbonate present.
ionic equation for sulfate test
Ba2+(aq) + SO4(2-)(aq) —— BaSO4 (s)
describe the test for sulfate ions
add barium nitrate to solution. If white precipitate forms sulfate ions are present
what are the sequence of tests
- carbonate, 2.sulfate, 3.halides
What is the order of the anion tests:
carbonate test is first as effervescence is observed unlike any of the others so no possible incorrect conclusion. Sulfate test second because a white precipitate also occur for carbonate and its already ruled out. Halide last and as precipitates also form so it would have to be a halide.
how would you carry out the tests if there is a mixture of ions
carry put tests for same sequence. for carbonate test add nitric acid till all bubbling stops (all carbonate ions removed). For sulfate test add excess Ba(NO3)2 and filter off precipitate. Halide test as normal
equation for ammonium ion test
NH4+(aq) + OH-(aq) —– NH3(g) + H2O(l)
describe ammonium ion test
NaOH is added to NH4+. NH3 gas is produced which is alkaline so using indicator paper it will turn blue
what is a disproportionation reaction
oxidation and reduction of the same element
example of disproportionation reaction with NaOH and Cl
Cl2(g) + 2NaOH(aq) —- NaClO(aq) + NaCl(aq) + H2O(l). NaOH must be cold and dilute.
example of disproportionation reaction with H2O and Cl
Cl2(g) + H2O(l) —- HClO(aq) + HCl (aq)
what is the use for chloric (I) acid
bactericidal so can disinfect or purify water
what are the risks associated with chlorinating water
chlorine can react with organic matter to form chlorinated hydrocarbons that can cause cancer. chlorine is a respiratory irritant
what is NaClO
bleach
energy change in the formation and breaking of bonds
energy supplied to break bonds. Energy released to form bonds
exothermic reactions
give out heat energy. Products have less energy than the reactants
endothermic reactions
takes heat. Products have more energy than the reactants
define activation energy
minimum energy required for a reaction to take place
energy change formula
Q=mc(change in)t
what is standard enthalpy change of a reaction
enthalpy change when the amount shown in the chemical equation react under standard conditions with the reactants and products in their standard states
what is standard enthalpy change of neutralization
the enthalpy change of reaction when amounts of an acid and an alkali react under standard conditions
what is the standard enthalpy change of combustion of a substance
enthalpy change when one mole of the substance completely burns in oxygen under standard conditions with the reactants and products in their standard solution
what is the standard enthalpy change of formation of a compound
enthalpy change when one mole of the compound forms from its elements under standard conditions with the elements and the compound in their standard states
what is the bond dissociation enthalpy
enthalpy change on breaking one mole of a particular covalent bond in a gaseous mole.
Describe the determination of an enthalpy change of combustion practical
- measure some water in a measuring cylinder. Pour into beaker and record initial temperature.
- Add methanol to spirit burner, weigh spirit burner containing ethanol.
- Place spirit burner under beaker. Light the burner and burn the methanol while stirring the water wth the thermometer.
- After 3 minutes extinguish flame and record max temperature reached.
- Reweigh the spirit burner
energy change of combustion formula
energy transferred to water / mol
enthalpy of combustion practical sources of error
heat loss to surroundings, incomplete combustion, evaporation of methanol, non-standard conditions (all lead to lower than expected results)
limitations of enthalpy change of neutralization experiment
heat loss to surroundings, under non-standard conditions and specific heat capacity of cup not taken into account.
what is the first law of thermodynamics
energy cannot be created or destroyed, only changed from one form to another
why are enthalpy changes measured under standard conditions and what are the standard conditions
data is compared so conditions need to be standardised to ensure nothing else is effecting the enthalpy changes. 298K. 100KPa
what is first electron affinity?
the energy released when 1 mole of gaseous atoms each acquire an electron to form 1 mole of gaseous 1- ions.
What is hess’ law
enthalpy change is independent of the route taken, providing the conditions are constant. If all but one enthalpy change is known then an expression can be formed to work out the missing enthalpy change
what factors affect rate
concentration, pressure, temperature, catalyst and surface area
what does increase concentration/pressure do to rate?
more particles in a given volume leads to higher frequency of successful collisions
what does increase temperature do to rate?
increase KE/ more particles have necessary activation energy therefore higher frequency of successful collisions
how can you measure the rate of reaction
volume of gas produced, mass of reactant and colour change
what is homogenous catalyst
catalyst in the same physical state as the reactants
what is heterogenous catalyst
catalyst in different physical state from the reactants
how does a catalyst speed up the rate of reaction
lowers activation energy by finding an alternative reaction pathway
what does the total area under the boltzmann distribution graph
total number of molecules
what is dynamic equilibrium
stage in a reversible reaction where the rate of the forward reaction is equal to the rate of the backwards reaction. Concentration of reactants/products stay the same
what is le chatelier’s principle
when a change is made to favour forwards or backwards reaction the system readjusts it to minimize the effects of that change.
how do we know a reaction hasn’t stopped during equilibrium
by using radioisotopes
what does equilibrium constant show
whether the reaction is more product or more reactant favored
what is the Kc formula for this reaction A+B —- 2C
[C]2 / [A][B]
what does it mean of Kc is greater than one
product favoured reaction
what does it mean of Kc is less than one
reactant favoured reaction
what can effect Kc
change in temperature
what are the labels for the axis on a boltzmann distribution graph
y axis - number of molecules with a given energy
x axis - energy
How does the boltzmann distribution graph depending on temperature. Why does this change occur
At higher temperature the peak is shifted to the right and the peak isn’t as high on the y axis. When it dips down the curve doesn’t dip as low as the lower temperature curve. More particles have activation energy so higher frequency of successful collisions.
How do you prepare a standard solution
- weigh the solid on a weighing boat.
- Solid is dissolved in a beaker using less water than is needed to fill the volumetric flask.
- Solution is transferred to a volumetric flask. Last traces of the solution are rinsed into the flask with distilled water.
- The flask is carefully filled to the graduation line by adding distilled water a drop at a time until the bottom of the meniscus lines up exactly with the mark.
- Volumetric flask is inverted several times to mix the contents.
