ThermochemistryThermochemistry
Study of heat in chemical reactions. Heat will travel between a system and
its surroundings Heat is measured in Joules (J) Metric English: BTU (British
Thermal Unit) 1 BTU = 1.06 kJ
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Calculating HeatCalculating Heat
The heat that transfers between substances can be calculated with the following equation:
q = (s) (m) (∆T)
Calculating HeatCalculating Heat
q : amount of heat (energy) transferred
s: specific heat m: mass (use density to change
from mL to g!) ∆T: change in temperature
Calculating HeatCalculating Heat
Specific Heat is the quantity of heat needed to raise one gram of a substance 1.0 ⁰C.
Each specific substance has its own specific heat. (pg. 394)
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Round to 4.18
Calculating HeatCalculating Heat
Example: How much heat is needed to
warm a 200.0 mL cup of coffee (H2O) from 20.0 ⁰C to 75.0 ⁰C?
Calculating HeatCalculating Heat
45980 J, but only 3 significant digits so….
4.60 x 104 J or 46.0 kJ
C))(55.0C g
J g)(4.18 (200.0 q o
Calculating HeatCalculating Heat
What is the specific heat of lead?
100.0 °C
20.0 °C
28.8 °C
1st Step - Calculate “q” for the H2O
C)20.0 - C)(28.8 C g
J g)(4.18 (50.0 q oo
q = 1840 J
20.0 °C
2nd Step - Calculate “s” for Lead
100.0 °C
q = (150.0 g)(s)(71.2oC)1840 J
Energy that water absorbed in step one was supplied
by the metal!
s = 0.172 J/(g x C) for Lead