3(a) Energetics

Question 1

exothermic reaction?

Answer 1

transfer energy to the surrondings

Question 2

endothermic?

Answer 2

take in hat energy from surrondings

Question 3

activation energy?

Answer 3

minimum amount of energy the reactant particles need in order to collide with each other and react (the higher it is, the more energy required to start the reaction)

Question 4

is a neutralization reaction exo or endo?

Answer 4

exothermic as energy is always given out

Question 5

is a displacement reaction exo or endo?

Answer 5

both as energy can be taken in or given out

Question 6

is a combustion reaction exo or endo?

Answer 6

exothermic

Question 7

calorimetry?

Answer 7

technique used to measure changes in enthalpy of chemical reactions (method to measure heat transfers)

Question 8

principle of calorimetry experiments?

Answer 8

to carry out the reaction with an excess of one reagent and measure the temperature change over the course of a few minutes (suitable for reactions like dissolving, displacement and neutralization)

Question 9

examples of what a calorimeter can be made up of?

Answer 9

• polystyrene drinking cup
• a vacuum flask
• metal can

Question 10

what does a polystyrene cup look like as a calorimeter?

Answer 10

• has a polystyrene cup
• reaction mixture
• thermometer
• plastic lid

Question 11

calorimetry experiments (reaction in solution)

Answer 11

• fixed volume of one reagent is added to the make-shift calorimeter - take initial temperature
• excess amount of 2nd regent is added and stir it
• max temperature recorded is the rise

Question 12

principle of enthalpy combustion expeierments?

Answer 12

to sue the heat released by combustion reaction increase the heat content of water

Question 13

calorimeter for to measure temperature change in combustion experiments?

Answer 13

• draught shield
• spirit burner
• copper can with water inside
• insulating lid
• thermometer

Question 14

how does a simple combustion calorimeter experiment occur?

Answer 14

• a fixed volume of water is measured and transferred to the copper can
• the spirit burner containing, for example, an alcohol, is weighted on a 2dp balance
• the initial temperature of water is measured and recorded
• the alcohol is ignited and the water is stirred continuously
• when the temp has risen by about 20 degrees the flame is extinguished and the spirit burner is re-weighed
• the final temperature of the water is recorded.

Question 15

specific heat capacity?

Answer 15

the energy needed to raise the temperature of 1g of substance by 1K

Question 16

energy transferred equation?

Answer 16

q = m x c x ∆T
q = the heat transferred (J)
m = the mass of water (g)
c the specific heat capacity
T = temp change in kelvin

Question 17

molar enthalpy change?

Answer 17

the heat energy change per mole of substance. It has the symbol ΔH and ahs the unit KJ per mole

Question 18

equation for molar enthalpy change?

Answer 18

ΔH = q / n
q heat change for the reaction
n = number of moles