January 14 Chemistry 11

In todays class we learned about calorimetry and molar enthalpy.

Calorimetry: to measure heat absorbed and released by water we have to find out three things:
1) temperature change degrees Celsius
2) amount of water g , kg , ml , L
3) heat capacity kJ/kg ° C the heat needed to change 1 degree in ° C is 1kg

ΔH = mCΔt will be the formula we will need to know.
the heat capacity of water is 4.19 kJ/kg° C

Example: a glass of water 250g is at 20 celsius it is placed on a stove and heated until it reaches a final temperature of 85 clesius, how much energy was added to the water?
m= .250kg change it to kg
c = 4.19
t = 85-20 temperature final - temperature initial
(.250)(4.19)(85-20) = 68.1kJ

Molar Enthalpy: heat absorbed/released by one mole (kJ/mol)

Example:
if there is 1g of wax burnt what is the amount of energy released?
C25H52 + 38O2 = 25CO2 + 26H2O + 11ookJ
convert grams to moles 1g = 1mol/352g molar mass of candle
= .00284mol
then we go .00284mol x 1100kJ / 1molC25H52 = 31.2 kJ/mol
Answer: 31.2 kJ/mol of energy is released when 1g of wax is used

Calirometry video:


Molar Enthapyl video: