Physical Chemistry

Question 1

Exothermic

Answer 1

releases heat to the surroundings, test tube feels cold

Question 2

endothermic

Answer 2

takes in heat from the surroundings, test tube feels hot

Question 3

examples of exothermic reactions

Answer 3

neutralisation, displacement and combustion reactions

Question 4

examples of endothermic reactions

Answer 4

displacement reactions

Question 5

calorimetry

Answer 5

used to measure changes in enthalpy of chemical reactions

two types: enthalpy changes of reactions in solution, enthalpy changes of combustion

Question 6

reactions in solution

Answer 6

• principle is to have an excess of one reagent and measure the temperature change over the course of a few minutes
• this technique is suitable for dissolving, displacement and neutralisation
• calorimeter can be made up of a polystyrene drinking cup, a vacuum flask or metal can
• fixed volume of one reagent is added to the calorimeter and the initial temperature is taken
• excess amount of second reagent is added and solution is stirred continuously
• maximum temp is recorded and temperature rise is calculated

Question 7

combustion experiments

Answer 7

• principle is to use the heat released by a combustion reaction to increase heat content of water
• fixed volume of water is poured in a copper can
• spirit burner, containing an alcohol is weighed on a balance
• initial temp is measured and recorded
• alcohol is ignited and water is stirred continuously
• when temp has increased by 20 degrees, flame is extinguished and spirit burner is re-weighted

Question 8

equation for heat energy change

Answer 8

q = m x c x ΔT
q = heat transferd
m = mass of water
c = specific heat capacity (4.2)
t = temperature change

Question 9

equation for molar enthalpy change

Answer 9

ΔH = q ÷ n 
q = heat energy change
n = number of moles

Question 10

exothermic energy level diagrams

Answer 10

energy of products is lower than reactants bc energy is released

Question 11

endothermic energy level diagrams

Answer 11

energy of products is higher than energy of reactants bc energy is taken in

Question 12

bond breaking

Answer 12

endothermic process bc it requires energy to break bonds

Question 13

bond forming

Answer 13

exothermic process bc it releases energy

Question 14

investigating temperature changes

Answer 14

• add solution n1 and record temp
• add solution n2, stir
• measure and record highest temperature reached by mixture

Question 15

dehydration of hydrated copper(II) sulfate

Answer 15

• copper (II) sulfate is a salt thaï contains water of crystallisation
• water of crystallisation is indicated with a dot between the salt and surrounding water molecules
• copper (II) sulfate can be dehydrated to form copper surface and water, but the reverse reaction produces hydrated copper(II) sulfate

Question 16

thermal decomposition of ammonium chloride

Answer 16

• produces ammonia and hydrogen chloride

- as the gases cool down they recombine to form solid ammonium chloride

Question 17

conditions needed for dynamic equilibrium to be reached

Answer 17

• concentration of reactants and products remains constant
• occurs in a closed system
• rate of forwards reaction is equal to rate of backwards reaction

Question 18

increase in temperature

Answer 18

equilibrium moves in the endothermic direction to reverse the change

Question 19

decrease in temperature

Answer 19

equilibrium moves in the exothermic direction to reverse the change

Question 20

increase in pressure

Answer 20

equilibrium shifts in the direction that produces the smaller number of gas molecules to decrease pressure

Question 21

decrease in pressure

Answer 21

equilibrium shifts in the direction that produces the larger number of gas molecules to decrease pressure

Question 22

effect of catalyst

Answer 22

does not affect the position of equilibrium but increases the rate at which equilibrium is reached