Heat &Heating Curves The change in the internal energy of a substance causes the change of phase. Energy Absorbed SOLID LIQUID GAS Energy Released

(always from higher to lower) Energy enters your hand from a hot stove because ___________ __________________________. If you touch ice, energy passes from ________ into _________. Heat (in joules)(J): energy transferred due to a temperature difference the stove is warmer than your hand your hand the ice (always from higher to lower)

(translational motion) (vibrational & rotational motion) Internal Energy: total of all KE + PE (translational motion) gas KE of moving molecules KE of moving atoms in molecules (vibrational & rotational motion) Internal Energy liquid & solid Demo – raise and drop textbook loudly (twice) PE stored in attractions (IMAFs)

The distance between particles. Ice melts by absorbing heat, but without increasing temperature. 0oC solid  0oC liquid (avg KE stays same) What changes? The distance between particles. (PE increases)

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

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

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

The phase change sequence is reversible. Cooling Curve of Water gas condensation 100oC boiling liquid The phase change sequence is reversible. Temp (oC) freezing 0oC melting solid Time (of Heat Added)

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

Quick Quiz. 3. Molecules with stronger IMAFs will have… higher heats of vaporization higher heats of fusion higher boiling points higher melting points higher viscosity higher specific heat capacity higher surface tension ALL of the above