Calorimetry
To measure heat absorbed/ released bywater, we need to know three things:
- Temperature change (° C)
- Amount of Water (g, kg, mL, L)
- Specific Heat Capacity (kJ/kg ° C)- the heat needed to change 1 degree C in 1 kg
Read as: Change in enthalpy is equal to the mass of water times the specific heat capacity times the change in temperature.
The specific heat capacity of water is 4.19 kJ/kg ° C
Ex: -calculate the amount of heat (in joules) required to warm 400g of water from 10°C to 35°C.(Heat Capacity (C) for H₂O is 4.18 kJ/ kg·°C) ***mr. doktor said 4.19 but it doesn't matter whether it's off by 1...- refer to Hand in Assignment #9 - energy in chemical reactions #7***
-When looking for a final temperature change (and other similar−) the equation can be (and is) rearranged using Algebra.
ΔH = mC(Tfinal - Tinitial)
Tfinal = (ΔH ÷ mC) + Tinitial
the answer gives you the final change in temperature.
Molar Enthalpy
- Heat absorbed/released by one mole (kJ/mol)
Example:
C25H52 + 38O₂ → 25CO₂ + 26H₂O +1100kJ
If there are 1.0g of wax burnt, what is the amount of energy (aka heat) released?
-Firstly you need to convert g to mol
1.0g = 1mol / 352g [352g is taken from the total mass of wax (C25H52)]
= 0.00284mol
- we take the Coefficient and us it like:
0.00284mol × 1100kJ / 1molC25H52 = 31.2 kJ/mol
Therefore: 31.2 kJ/mol of energy are released when 1.0g of wax is burnt (used up)
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Here's a site on caliometry:
Here's a site on caliometry and molar enthalpy:
And here's a video on someone solving a caliometry question:
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