[9.2] measuring enthalpy changes

Question 1

what equation is used to determine the amount of energy transferred to the surroundings?

Answer 1

q = mcΔT

Question 2

what are the units for q = mcΔT?

Answer 2

q = heat energy transferred (J)
m = mass of substance heated (ie. liquid) (g)
c = specific heat capacity, it is a constant, which is 4.18
ΔT = temperature change. don’t need to convert between kelvin and celcius because you want the temperature change

Question 3

what is the equation which is used to convert the heat energy, q (J) to enthalpy change, ΔH (kJ mol-1)

Answer 3

ΔH = q / n

(make sure to divide q by 1000 because ΔH is in kJ, not J, always use 3sf)

Question 3

why might the experimental ΔH value not be accurate?

Answer 3

• heat loss to the surroundings
• incomplete combustion
• evaporation of (methanol) from the wick
• non-standard conditions

Question 4

what are calorimetry extrapolations?

Answer 4

when you extrapolate the graphs to the time of mixing reagents to find the temperature change. it is more accurate than calculating the difference between the maximum and minimum temperatures for reasons unknown