Chemistry is about to heat up… Please get out: 1.Last Large Group Notes 2.This Large Group Notes 3.Calculator THERMOCHEMISTRY

 Chemical Potential Energy  Energy in chemical bonds  Thermal Energy  Kinetic energy of molecules  This has to do with heat!  HEAT  What this part is about TYPES OF ENERGY

 Heat will always flow from a hot substance to a cold substance  Temperature is not Heat  Temperature  Average kinetic energy  Heat  A form of energy  Think of a car driving down the road  A car has a temperature, but it also has kinetic energy  We do not say ‘The car is going 77°F’  Just like we don’t say ‘The jar has 40°C of heat’ HEAT

 Endothermic  Takes energy (usually cold)  Will absorb energy from surroundings  Exothermic  Releases energy (usually hot)  Will release energy to surrounding EXOTHERMIC/ENDOTHERMIC

 System  What we are concerned with  Surroundings  Everything else  Is this exothermic or endothermic?  Endothermic!  The water in the pot absorbs heat from the burner underneath it SYSTEM AND SURROUNDING System

 Many Xbox 360’s overheated and broke.  Identify the system and surrounding  Identify Exothermic or Endothermic  The Xbox releases energy to the surroundings SYSTEM VS SURROUNDINGS System

 You are probably familiar with one of the most popular: Calories  Note the big ‘C’  A Calorie is a food calorie  A calorie is the amount of energy required to heat 1 gram of water 1°C  A Calorie is 1,000 calories  Note the little ‘c’  Saying “Two tablespoons of Nutella has 200 Calories is really saying Nutella has 200,000 calories (!) UNITS

 The unit we will use most often is a Joule (J)  Or kiloJoule, 1 kJ = 1000 J  Joules = 1 calorie  Conversion Time!  How many Joules are in the 200,000 calories of Nutella?  Or… 836,800 Joules = kJ  That’s the same amount of energy as me moving at 319 mph MORE UNITS

 Heat Capacity (J/°C)  The heat required to raise the temperature 1°C  Specific Heat (J/g*°C)  Heat required to raise the temperature of 1 gram of something 1°C  EVERY substance has a different Specific Heat SPECIFIC HEAT Specific Heat of Wood Specific heat of Steel 2 J/g*°C0.49 J/g*°C

CALCULATING HEAT Joules Or Calories grams

CALCULATING SPECIFIC HEAT Mass Heat Change in Temperature

 2 kg of aluminum is heated from 20 o C to 100 o C. The specific heat of aluminum is 0.91 kJ/kg 0 C.  How much heat is required? q=mCΔTq=mCΔT  q=(0.91 kJ/kg 0 C)(2 kg)(100 0 C-20 0 C)  q= kJ MORE CALCULATIONS Mass Change in Temperature Specific Heat

CALCULATING HEAT Mass Change in Temperature Specific Heat

MORE FUN Mass Specific Heat Heat

 Does it take energy to change state?  Of course!  Heat of fusion/solidification  Solidification = liquid to solid  Fusion = solid to liquid  Does it take more energy to melt an ice cube than to freeze and ice cube?  It’s the same!  Heat of fusion (ΔH fus ) = -Heat of solidification (ΔH solid )  Freezing an ice cube Melting an ice cube CHANGE OF STATE J/g J/g

I DO

WE DO

 Vaporization and condensation work the same way.  Vaporization = liquid to vapor  Condensation = vapor to liquid  Heat of vaporization = -Heat of condensation  ΔH vap = -ΔH cond  What is this energy from?  Changing state means increasing the kinetic energy of the molecules enough to overcome the intermolecular bonds.  Or decreasing the kinetic energy enough such that the intermolecular bonds can hold the molecules together JUST LIKE BEFORE

BURNING MONEY

COMBINING PHASE CHANGE + TEMP CHANGE

 You’re drink has a 40 gram ice cube (0°C) in it. After 20 minutes the temperature of the ice is 25°C (oh no!). How much heat did the ice gain?  The heat of fusion of ice is J/gram  The specific heat of water is J/g*°C  Two Steps  Which steps?  Look at this:  Key words:  Ice (0°C)  25°C MELT AND HEAT

DA MATH 1) Melt 2) Heat

STEAM 25˚C 100˚C 120˚C 1 ) Heat 2 ) Boil 3 ) Heat

 1) Heat q=mCΔTq=mCΔT  q1 = (2000 grams)  q1 = 627,600 Joules (or kJ)  2) Boil  q = mH v  q2 = (2000 grams)  q2 = 4,514,000 Joules (or 4,514 kJ)  3) Heat q=mCΔTq=mCΔT  q3 = (2000 grams)  q3 = 75,600 Joules (or 75.6 kJ)  Add them up! THE MATH