Warm Up: Get out Reaction Diagram Paper Today: MORE NOTES!  Learning Targets: I can calculate the heat needed to run phase changes I can determine the specific heat of unknown substances Homework: Calorimetry Practice (back of notes)

Radiant Mechanical Electric Nuclear Chemical Sound Thermal Elastic Magnetic

The Role of Heat in Chemistry

Units of Energy calorie (cal) = the amount of energy it takes to raise 1 g of water by 1ºC Calorie (Cal) = 1000 calories Joule (J) = metric (SI) unit for energy 1 cal = 4.184 J Kilojoule (kJ) = 1000 Joules

Enthalpy (H) 286 kJ/mole How much heat energy an object contains (measured in kilojoules per mole) 236 kJ/mole 242 kJ/mole

Enthalpy (H) 286 kJ - 242 kJ = + 44 kJ 286 kJ/mole how much energy will be transferred when a mole of water changes to a mole of steam? 236 kJ/mole 286 kJ - 242 kJ = + 44 kJ 242 kJ/mole (heat must go in)

Enthalpy (H) 472 kJ - 572 kJ = - 100 kJ 286 kJ/mole how much energy will be transferred when two moles of steam changes to two moles of ice? 236 kJ/mole 472 kJ - 572 kJ = - 100 kJ 242 kJ/mole (heat must go out)

energy in = + ΔH energy out = - ΔH endothermic exothermic

Entropy Entropy is a measure of randomness or disorder.

Is Entropy Increasing or Decreasing? Leaving a hot cup of coffee out on the desk Leaving an ice cube out on the desk A lake freezing over in the winter Burning gasoline to make your car run Cutting a piece of paper into confetti Cleaning your room

System is getting more ORDERED, so entropy decreases Entropy in Chemistry In the following equation, is entropy increasing or decreasing? 2 H2 (g) + O2 (g) 2 H2O (l) 3 moles of GAS 2 moles of LIQUID System is getting more ORDERED, so entropy decreases

(+) (-) Enthalpy (ΔH) Entropy Conclusions Endothermic Exothermic Increasing disorder Decreasing disorder (more order)

Calorimeters Heat = mΔTCp or q

Ex. #1: When MgSO4 dissolves in 15.0 mL of water (d = 1.00 g/mL) at 25°C, 1.51 kJ of heat is evolved Is the process endothermic or exothermic? Write a balanced equation What is qH2O? What is the final temperature of the solution? (cp of H2O = 4.18J/g°C)

Ex. #3: Burning 1.00mL of isooctane (d = 0.688g/mL) releases 33.0 kJ of heat. When 10.0 mL of isooctane is burned in a bomb calorimeter, the temperature in the bomb rises from 23.2°C to 66.5°C. What is the heat capacity of the calorimeter?

Calculating heat for physical changes boiling point melting point

Heat of fusion/vaporization The heat involved in changing state of matter DHfus = Heat of fusion heat required to melt/freeze 1 mole or 1 gram of a substance DHvap = heat of vaporization heat required to evaporate/condense a 1 mole or 1 gram of a substance Positive if warming Negative if cooling

Using heating curves For warming/cooling, q = mc∆T m = mass cp = specific heat capacity ∆T = change in temp (negative if cooling, positive if warming For phase change, q = (m or n)DHfus or q = (m or n)DHvap n = moles Hfus = Heat of fusion Hvap = heat of vaporization You will choose mass or moles based on units given for DHfus/DHvap

Ex. #2: Calculate the amount of heat involved in changing 10.0 g of liquid Br2 at 22.5°C to vapor at 59.0°C. m.p. = -7ºC DHfus = 10.8 kJ/mol b.p. = 59ºC DHvap = 29.6 kJ/mol Cp = 0.474 J/gºC