Periodic Table And Energy

Question 1

Periodic table then

Answer 1

Mendeleev arranged elements in order of atomic mass
-also lined up elements with similar properties
-left gaps assuming some were yet to be discovered

Question 2

Trends across a period

Answer 2

same number of shells
- different number of electrons in outer shell

Question 3

Trends down a group

Answer 3

Same number of electrons in outer shell
-number of shells increase (shielding)
-atomic radius increases

Question 4

Ionisation energy

Answer 4

how easily an atom loses electrons to form positive ions
-atomic radius increases i energy decreases
-nuclear charge increases I energy increases
-electron shielding increases i energy decreases

Question 5

Successive ionisation energies

Answer 5

He(g) —> He+(g) + e-
He+(g) —> He2+(g) + e-

Question 6

Second ionisation energy

Answer 6

energy required to remove one electron from each ion in 1 mole of gaseous 1+ ions of an element to form one mole of gaseous 2+ ions

Question 7

1st ionisation trends

Answer 7

across period- (increases)
nuclear charge increases⬆️
nuclear attraction increases⬆️
atomic radius decreases🔻

Down group- (decreases)
atomic radius increases
shielding ⬆️
nuclear attraction🔻

Question 8

giant covalent structures

Answer 8

-insoluble in most solvents
-do not conduct electricity
(except graphene & graphite)
-high melting & boiling points

Question 9

trends in melting point (period 2)

Answer 9

-Li –> C increases (giant structures)
-decreases dramatically to N as they are simple molecules so easier to overcome bonds

Question 10

trends in melting point (period 3)

Answer 10

Na –> Si increases as they are giant structures and atomic charge increases
-decreases dramatically to P as it is now simple molecules

Question 11

group 7 halogens

Answer 11

electronegativity decreases as you move down
-number shells increases
-weaker attraction
-BP increases as you move down
-more electrons and more induced dipoles (harder to break)

Question 12

halogen colours

Answer 12

fluorine-pale yellow gas
chlorine- yellow green gas
bromine - dark red/brown liquid
iodine - grey black solid
astatine- very rare & radioactive solid

Question 13

qualitative analysis of halide ions

Answer 13

-add nitric acid to get ride of carbonate ions
-then add silver nitrate
fluoride- no precipitate
chloride-white precipitate (dissolves in dilute NH3)
bromide-cream precipitate (dissolves in conc NH3)
iodide-pale yellow precipitate ( does not dissolve in either)

Question 14

Qualitative analysis of sulphate ions

Answer 14

Sulfate ions
- dilute nitric acid (remove carbonate ions) + barium nitrate
white preciptate BaSO4 formed

Question 15

qualitative analysis of carbonate ions

Answer 15

carbonate ions
-add dilute nitric acid; if bubbles form product could be carbonate
-check if CO2 bubble thru limewater (cloudy)

Question 16

Enthalpy H

Answer 16

measurement of the heat energy in a chemical system
ethalpy change = H(products) - H(reactants)

Question 17

endothermic reaction

Answer 17

heat into system from surroundings
system gains temp
-surroundings temp decreases
-bond breaking energy required

Question 18

exothermic reaction

Answer 18

-bond making
heat transferred to surroundings from system
loses heat (temp drops)
-temp of surroundings increases

Question 19

standard enthalpy change conditions

Answer 19

pressure= 100kpa
temp= 25 c
conc= 1moldm3
state=physical state normally

Question 20

standard enthalpy change of reaction

Answer 20

enthalpy change that accompanies a reaction in the molar quantities shown in chemical equation under standard conditions

Question 21

standard enthalpy of formation

Answer 21

enthalpy change that takes place when 1 mole of a compound is formed from its elements under standard conditions
1/2 O2 to make the product 1 mole only

Question 22

standard enthalpy of combustion

Answer 22

the enthalpy change that takes place when one mole of a substance reacts completely with oxygen under standard conditions

Question 23

standard enthalpy change of neutralisation

Answer 23

the enthalpy change that accompanies the reaction of an acid and a base to form one mole of water under standard conditions

Question 24

q=mc^T

Answer 24

q= energy change of surroundings
m= mass of surroundings
c= specific heat capacity (4.18kjg-1k-1)
^T= change in temp
if - = endothermic
if + = exothermic
q/n to see per mole of the reactant
opposite to answer +/- as now talking about reactant heat loss or gain

Question 25

HESS law

Answer 25

states that reaction can take place by 2 routes and the total enthalpy change is the same for either route
triangle
A-B = ^H1
A-C-B = ^H2 + H3
elements - arrows go away
products - either
combustion - arrows go towards

Question 26

rate of reaction

Answer 26

measures how fast a reactant is being used up or how fast a product is formed
change in conc / time

Question 27

increasing gas pressure effect on rate

Answer 27

when gas is pressed into smaller volume the pressure of a gas is increased and the rate of reaction increases

Question 28

catalysts

Answer 28

a substance that changes the rate of a chemical reaction without undergoing any permanent change itself
- catalyst not used up in reaction
- always regenerated

Question 29

homogenous catalyst

Answer 29

catalyst that is the same physical state as the reactants

Question 30

heterogenous catalyst

Answer 30

catalyst that is in a different physical state to the reactants

Question 31

Boltzmann distribution (temp)

Answer 31

as temperature increases a higher proportion of molecules can overcome the activation energy
-more successful collisions

Question 32

boltzmann distribution ( catalyst)

Answer 32

when a catalyst added, greater proportion of molecules exceed the new lower activation energy
lower activation energy

Question 33

Dynamic equilibrium

Answer 33

the rate of the forward reaction is the same as the rate of the backwards reaction
- concentration of products does not change

Question 34

le chateliers principle

Answer 34

states that when a system in equilibrium is subjected to an external change the system readjusts itself to minimize the affect of the change