Transcript PowerPoint - Thermochemistry, Heat Capacity, and Calorimetry

Specific heat capacity (a.k.a. Specific heat)
• symbolized as c, units in J/gC
• It’s the heat required to raise 1 gram of a
substance by 1 C
Heat capacity
• calculated by c x m, units in J/C
• It’s the heat required to raise the temperature
of an object by 1 C.
Molar heat capacity
• Similar to specific heat capacity, but uses
moles instead of grams, units in J/mol C.
• It’s the heat required to raise the temperature
of 1 mol of a substance by 1 C
Answers
2.
a) As calculated yesterday: 25.5 kJ
b) Specific heat is 4.18 J/gC (pg. 151)
c) Heat capacity: cm=4.18J/gCx200g=836 J/C
d) Molar heat capacity is c x g/mol
=4.18 J/gC x 18 g/mol = 75.3 J/molC
3. Simply using q=cmT,
c= 4.18 J/gC, m=335 g, T=26.4-24.5= 1.9C
q=cmT= 4.18 J/gC x 335 g x 1.9C = 2.7 kJ
4. We cannot determine the c for wax from this
data because we did not heat the candle (no
value for T). We would have to change the
lab procedure if we wanted c for wax.
5. q=cmT= 2.0 J/gC x 5 g x 60 C = 600 J
6. q=cmT,
c=q/mT= 10 J /(3.1 g)(17.9C) = 0.18 J/gC
(gold is 0.129 J/gC - pg. 151; it is not pure)
heat capacity
= cm = 0.18 J/gC x 3.1 g
= 0.558 J/ C
5.15: Something with a high c needs more
energy to increase in temperature
5.16: Something with a low c experiences a
greater rise in temp. given the same energy
5.18: The body is mostly water. Water (and the
body) has a high c, thus a large change in
energy will cause only a small shift in temp.
Crossword
8. negative
9. positive
11. grams
12. bomb
14. law of
conservation of
energy
17. insulator
18. endothermic
19. oxygen
20. water
1.
2.
3.
4.
5.
6.
7.
10.
13.
15.
16.
enthalpy change
thermochemistry
calorimeter
heat of reaction
exothermic
out
surroundings
boundary
enthalpy
system
coffeecup
9.
Enthalpy (total energy) includes:
chemical potential energy of chemicals
gravitational potential energy
kinetic energy (earth’s rotation, etc)
heat energy
We cannot measure enthalpy because we
cannot measure absolute gravitational or
kinetic energy
10.Any reaction that produces light, sound,
kinetic energy (explosion), etc.
11.
Thermometer identifies T of water. H is found
using q=cmT and law of conservation of
energy (technically, pressure must be
constant for q to equal H)
Boundary
Endothermic
Exothermic
System
A basic calorimeter - see handout
• In our lab we tried to determine H via q from
“calorimetry”. Here are some terms associated with calorimetry (and thermochemistry)
Surroundings
everything else
System with
can as
boundary
Endothermic =
absorbing energy
Exothermic =
releasing energy
Law of conservation of energy = release and
absorption of energy must be equal
For more lessons, visit
www.chalkbored.com