Group Two and Enthalpy Change

Question 0

What is the trend in electronegativity down group 2?

Answer 0

It decreases

More electrons, more shielding, weaker attraction between positive nucleus and outer electron which is higher in energy

Question 1

What is the trend in ionisation energy down group 2?

Answer 1

It decreases

More electrons, more shielding, weaker attraction between positive nucleus and outer electron which is higher in energy

Question 2

What is the trend in melting point down group 2?

Answer 2

It generally decreases however increases from Mg to Ca
Ions increase in size after Mg leading to weaker metallic bonds, Mg has a different structure that is more closely compact

Question 3

What is the trend in atomic radius down group 2?

Answer 3

It increases

More electrons, more shielding

Question 4

What is the trend in reactivity down group 2?

Answer 4

It increases

Outer two electrons are more easily lost

Question 5

Describe the reactivity of Mg

Answer 5

Reacts slowly with water

But vigorously with steam, very exothermic, producing Magnesium Hydroxide

Question 6

Describe the reactivity of Ca

Answer 6

fizzing with cold water to form Calcium Hydroxide and hydrogen

Question 7

Describe the reactivity of Sr

Answer 7

Stored under oil to prevent reaction with air
Vigorously with water to form a colourless solution
Strontium Hydroxide

Question 8

Describe the reactivity of Ba

Answer 8

Similar reaction with water to Sr

Forms Barium Hydroxide

Question 9

How does magnesium react with H2SO4

Answer 9

Less dense than water
Reacts until dissolved
Hydrogen gas
Forms soluble precipitate Magnesium Sulphate

Question 10

How does Calcium react with H2SO4

Answer 10

More dense than water
Produces an insoluble precipitate coating Calcium Sulphate white
Hydrogen gas
Calcium is more reactive than magnesium

Question 11

What is the trend in solubility in the hydroxides of group 2

Answer 11

The hydroxides become less soluble up the group

Question 12

What is the trend in sulphates in group 2

Answer 12

They become less soluble as you go down the group

Question 13

What is a use for Magnesium Hydroxide

Answer 13

Milk of magnesia - anti acid that neutralises stomach acid

Relieves the symptoms of heartburn and indigestion

Question 14

What is a use for Calcium Hydroxide

Answer 14

‘Lime’ fields to control the acidity of the soil
Powdered limestone, calcium oxide, calcium hydroxide
Ensures soil pH optimum for crop

Question 15

What is a use of Barium Sulphate

Answer 15

Soluble barium compounds are toxic and absorbed through the intestines
Barium sulphate is insoluble in water
Contrast medium in medical X-rays of the digestive system

Question 16

Define standard molar enthalpy change if dissociation

Answer 16

Enthalpy change when one mole of bonds of the same type are broken in gaseous molecules under standard conditions averaged across a range of molecules

Question 17

What are the properties of an exothermic reaction

Answer 17

Negative enthalpy change
Temp increase
Enthalpy products smaller than reactants 
Heat lost to surroundings 
Temp reading increase/beaker feels warm

Question 18

What are the properties of an endothermic reaction

Answer 18

Positive enthalpy change
Temp decrease
Enthalpy of products higher than reactants 
Heat gained from surroundings
Temp decrease/beaker feels cold

Question 19

What is the equation for enthalpy change

Answer 19

Bonds broken - bonds made

remember to draw all bonds to ensure none are missed

Question 20

Define enthalpy

Answer 20

Measure of the heat contents of a substance

Question 21

Define enthalpy change

Answer 21

Change in heat content at a constant pressure

Question 22

What are the standard conditions for an enthalpy change

Answer 22

100KPa and a stated temperature

Question 23

Define enthalpy change of formation

Answer 23

Enthalpy change when one mole of a substance is formed from its constituent elements with all reactants and products in standard states under standard conditions

Question 24

Define standard enthalpy of combustion

Answer 24

Enthalpy change when one mole of a substance is completely burned in oxygen up withal reactants and products in standard conditions

Question 25

What is the equation for heat energy given out

Answer 25

q=mc

Question 26

What is the equation for enthalpy change per mole

Answer 26

q / number moles reacting

Always negative value if increase in temp as exothermic

Question 27

How do you calculate the excess of a substance in calorimetry

Answer 27

Calculate the substance which has he greatest number of moles

Question 28

What can heat loss in calorimetry lead to

Answer 28

Errors in results which is reduced through measuring the heat capacity of the calorimeter as a whole

Question 29

How can enthalpy changes be measured in reactions in a solution

Answer 29

Insulated polystyrene beaker
Thermometer to measure temp change
Burn a known mass of reactants in air and measure temp change

Question 30

How can enthalpy changes be measured in a flame calorimeter

Answer 30

Copper calorimeter
Find enthalpy combustion of a substance
Burn a known mass of reactants in air and measure temp change

Question 31

How can enthalpy changes be measured in a bomb calorimeter?

Answer 31

Most accurate
Known mass if fuel placed inside a steel container and the container is filled with oxygen under pressure
Fuel electrically ignited and heat evolved used to heat surrounding water
Heat capacity found by burning a substance wi accurately known

Question 32

What is Hess’s Law?

Answer 32

Enthalpy change is independent of the route taken

Question 33

What is the equation for flying pigs?

Answer 33

Formation (products) - formation (reactants)

Question 34

When should flying pigs be used?

Answer 34

It should be used when given formation values

Products - reactants

Question 35

What is the equation for cranky rhinos?

Answer 35

Combustion (reactants) - combustion (products)

Question 36

When should cranky rhinos be used?

Answer 36

It should be used when asked to calculate formation when given combustion
(Reactants - products)

Question 37

Define mean bond enthalpy

Answer 37

The amount of energy required to break a covalent bond averaged over a number of different compounds