Section 4: Heat & Calorimetry

+ 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. + 4.18 J of heat c (water) = ________ 4.18 J/goC

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) http://www.videopediaworld.com/video/28266/Heat-And-States-Of-Matter-Heat-Capacity (2 min)

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

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)

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

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

Quick Quiz. 2. How many joules would it take to raise 10 grams of liquid water from 20oC to 30oC? 2090 J 418 J 209 J 41.8 J + 4.18 J