Heat, Calorimetry, & Heating Curves Energy Absorbed (Endothermic) SOLID LIQUID GAS Energy Released (Exothermic)

Heat = “transfer4ed” thermal energy 80oC heat 20oC It’s incorrect to say matter “contains” heat. Matter “contains” KE and PE. Energy of Motion Stored Energy (moving or vibrating) (bonds & attractions) Thermal Energy Chemical Energy

WHY? Describe: The same amount of heat is added to each container, but the temperature of the container with less water increases more. Explain: avg Temp is higher b/c it’s a measure of _____ KE per particle.

+ 4.18 J of heat specific heat capacity(c): heat to change 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)

Substance (J/goC) 4.18 water has a high c ! Water (l) 4.18 Aluminum (s) 0.900 (demo) 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 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 = 160,000 J

Ice melts by absorbing heat, but without increasing temperature. 0oC solid  0oC liquid (avg KE stays same) HOW? …by changing phase.

added heat breaks IMAFs & increases distance (↑PE) Heating Curve same temp during phase change (=KEavg) What happens to added heat? vaporize/condense added heat breaks IMAFs & increases distance (↑PE) VLC – media file (Changes of State) melt/freeze

Heating Curve of Water KE PE KE PE handout KE PE heat raises Temp endothermic (↑KE) gas exothermic KE PE boiling 100oC boiling point condensation (↑PE) heat breaks IMAFs liquid Temp (oC) heat breaks IMAFs (↑KE) heat raises Temp (↑PE) melting melting point 0oC freezing freezing point solid (↑KE) heat raises Temp Time (or Heat Added)

c = 4.18 J/goC (liquid water) Heating Curve of Water handout Why is ∆Hvap >>> ∆Hfus? heat of vaporization LG takes more energy to break IMAFs than SL gas (2260 J/g) 100oC (∆Hvap) heat required to vaporize (or condense) liquid Temp (oC) heat of fusion (418 J/g) c = 4.18 J/goC (liquid water) (334 J/g) 0oC (∆Hfus) heat required to melt (or freeze) solid Time (or Heat Added)

The phase change sequence is reversible. Cooling Curve of Water As a form of energy, heat has the unit joule (J) in the International System of Units (SI). ... Heat released by a system into its surroundings is by convention a negative quantity (Q < 0); when a system absorbs heat from its surroundings, it is positive (Q gas condensation 100oC boiling liquid The phase change sequence is reversible. Temp (oC) freezing 0oC melting solid Time (or Heat Removed)

As a form of energy, heat has the unit joule (J)...  Heat released by a system into its surroundings is a negative quantity (Q < 0); when a system absorbs heat from its surroundings, it is positive (Q> 0).

animation

Quick Quiz! Temperature is directly proportional to the _________ of a substance. thermal energy vibrational kinetic energy average kinetic energy total kinetic energy

Quick Quiz. Heat is simply another word for _________. temperature internal energy energy transferred from hot to cold thermal energy transferred

Quick Quiz. 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. 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