4/30 Opener Identify the following reactions as endo or exothermic: IMPORTANT! All April work must be turned into me by Friday 5/4. This includes both titration labs. I will send out a report today! Junior meeting tomorrow at 2:30-Chat about prom & class t-shirts 

Define Heat Compare Endothermic and Exothermic reactions Know units Thermochemistry Define Heat Compare Endothermic and Exothermic reactions Know units

Heat Represented by q One effect of adding heat to an object in an increase in its temperature Heat always flows from a warmer object to a cooler object

Processes System – the part of the universe on which you focus your attention Surroundings – everything else in the universe Law of Conservation of Energy – in any chemical and physical process, energy is neither created or destroyed

Heat Capacity and Specific Heat Heat capacity depends on the mass and chemical composition of the object Specific heat is the amount of heat it takes to raise the temperature of 1g by 1°C C = q ___ or = ________heat__________ m x ∆T mass(g) x change in °C

Plicker Review In what direction does heat flow? A. Forward B. High to Low C. Low to High D. Up The part of the universe on which you focus your attention is called: A. Surroundings B. Earth C. System D. Energy Region In what process does the system gains heat as the surroundings cool down? Endothermic B. Caloric C. Exothermic D. Potential In what process does the system lose heat as the surroundings heat up? A. Endothermic B. Caloric C. Exothermic D. Potential

Measuring and Expressing Enthalpy Changes SWBAT: Describe Calorimetry Use Thermochemical Equations

Calorimetry The precise measurement of the heat flow into or out of a system for chemical or physical processes. Enthalpy (H) of the system is the heat content of a system at constant pressure A calorimeter is an insulated device used to measure the absorption or release of heat in chemical or physical processes Constant-Pressure Calorimeters – foam cups which do not let much heat in or out, open to the atmosphere. Measures enthalpy (H), q = ∆H qsys = ∆H = -qsurr = -m x C x ∆T Negative ∆H values are exothermic reactions, while positive ∆H values are endothermic Constant-Volume Calorimeters, or bomb calorimeter

Complete Model 3

Enthalpy Calculation When 25ml of water containing .025mol of HCL at 25*C is added to 25.0 ml of water containing .025mol of NaOH at 25*C in a calorimeter a reaction occurs. Calculate the enthalpy change in joules if the highest temperature observed is 32*C. -731 J

Thermochemical Equations In a chemical equation, the enthalpy change for the reaction can be written as either a reactant or a product A thermochemical equation includes the enthalpy change The heat of reaction is the enthalpy change for the chemical equation exactly as it is written The heat of combustion is the heat of reaction for the complete burning of one mole of a substance.

Using Heat of Reaction to Calculate Enthalpy Change 2NaHCO3(s) + 129KJ Na2CO3(s)+H2O(g)+ CO2(g) Is this reaction exothermic or endothermic? Calculate the amount of heat required to decompose 2.24 mol NaHCO3.

CH4 + 2O2 → CO2 + 2H2O + 802.2 kJ If 10.3 grams of CH4 are burned completely, how much heat will be produced? 514 kJ

CH4 + 2O2 → CO2 + 2H2O + 802.2 kJ How many liters of O2 at STP would be required to produce 23 kJ of heat? How many grams of water would be produced with 506 kJ of heat?

Heats of Fusion and Solidification Molar Heat of Fusion (Hfus) - the heat absorbed by one mole of a substance in melting from a solid to a liquid Molar Heat of Solidification (Hsolid) - heat lost when one mole of liquid solidifies

Heats of Vaporization and Condensation Molar Heat of Vaporization (Hvap) - the amount of heat necessary to vaporize one mole of a given liquid. Molar Heat of Condensation (Hcond) - amount of heat released when one mole of vapor condenses Hvap = - Hcond

Hess’s Law Hess’s law allows you to determine the heat of reaction indirectly Hess’s law of heat summation states that if you add two or more thermochemical equations to give a final equation, then you can also add the heats to give a final heat. Useful in calculating the heat of formation for just one of multiple products

Calculating Enthalpy Change Find the enthalpy change for the conversion of diamond to graphite. C(s, graphite) + O2(g)CO2(g) ΔHf=-393.5KJ C(s, diamond) + O2(g)CO2(g) ΔHf=-395.4KJ CO2(g) C(s, graphite) + O2(g) ΔHf=393.5KJ C(s, diamond) + O2(g) CO2(g) ΔHf=-395.4KJ C(s, diamond) C(s, graphite) ΔHf= -1.9KJ

Standard Heats of Formation The standard heat of formation (∆Hf0) of a compound is the change in enthalpy that accompanies the formation of one mole of a compound from its elements with all substances in their standard states at 25˚C For a reaction that occurs at standard conditions, you can calculate the heat of reaction by using standard heats of formation ∆H0 = ∆Hf0(products) - ∆Hf0(reactants)

Calculating Standard Heat of Reaction What is the standard heat of the reaction for : 2CO(g) + O2(g)CO2(g) CO(g) ΔHf= -110.5 O2(g) ΔHf= 0 CO2(g) ΔHf= -393.5