1. Section 4: Heat & Calorimetry

2. + 4.18 J of heat specific heat capacity(c):
heat required to raise 1 gram by 1oC
Different substances have different capacities for storing energy.
The water in food holds 4x the energy as an aluminum pan.
J of heat
c (water) = ________
4.18 J/goC

3. Specific Heat Capacities
Water absorbs/releases a lot of heat for a small ∆T.
(change in temp)
Water has a high c !
Specific Heat Capacities
Substance
(J/goC)
Water (l)
4.18
Olive oil (l)
1.97
Aluminum (s)
0.900
Steel (iron) (s)
0.450
Copper (s)
0.385
Mercury (l)
0.140
Lead (s)
0.129
Gold (s)
Why?
1 g of water requires
more heat than
1 g of metal for
every 1oC change.
(higher specific heat capacity)
(2 min)

4. Substance (J/goC) 4.18 water has a high c !
Water (l)
4.18
Aluminum (s)
0.900
Al metal atoms vibrate in place
Water “soaks up” (stores) a lot of energy in
intramolecular movements and
intermolecular attractions (H-bonds)
without changing average KE (Temp)
water has a high c !
Demo – burning dollar bill (50/50 mix of H2O/C2H5OH) Demo – Boiling water in paper cup
vibrating
stretching
stretching
rotating

5. Calorimetry q = mcT Heat transferred can be measured and calculated.
q = heat (J)
m = mass (g)
c = specific heat (J/goC)
(4.18 J/goC for water)
∆T = change in T
(Tfinal – Tinitial)

6. Sample Calculation: q = mcT
How much heat is needed to warm 500 g of water from 25 oC to 100 oC?
q = mcT
c = 4.18 J/goC
q = (500)(4.18)(100 – 25)
q = 157,000 J

7. Quick Quiz.
1. How much energy would it take to raise gram of liquid water from 20oC to 30oC?
4.18 J
20.9 J
41.8 J
209 J J

8. Quick Quiz.
2. How many joules would it take to raise grams of liquid water from 20oC to 30oC?
2090 J
418 J
209 J
41.8 J J