THERMODYNAMICS Courtesy of lab-initio.com

Definitions #1 Energy: The capacity to do work or produce heat (sum of P.E. and K.E) Potential Energy: Energy due to position or composition (in bonds) Kinetic Energy: Energy due to the motion of the object (particles proportional to energy)

Definitions #2 Law of Conservation of Energy: Energy can neither be created nor destroyed, but can be converted between forms (energy of universe is constant) The First Law of Thermodynamics: The total energy content of the universe is constant

Heat- involves a transfer of energy between two objects due to a temperature difference.

The system is our reaction. The surroundings are everything else.

 E = q + w  E = change in internal energy of a system q = heat flowing into or out of the system -q if energy is leaving to the surroundings +q if energy is entering from the surroundings w = work done by, or on, the system -w if work is done by the system on the surroundings +w if work is done on the system by the surroundings

Example ~  E : Calculate  E if q =  50 kJ and w = +35kJ.  q + w =  =  15 kJ

NMSI # 1: Energy Practice Calculate change of energy for a system undergoing an endothermic process in which 15.6 kJ of heat flows and where 1.4 kJ of work is done on the system.

Work, Pressure, and Volume Expansion Compression +  V (increase) -  V (decrease) - w results+ w results E system decreases Work has been done by the system on the surroundings E system increases Work has been done on the system by the surroundings

Example~WORK: Calculate the work if the volume of a gas is increased from 15 mL to 2.0 L at a constant pressure of 1.5 atm. w =  P  V w =  1.5 atm (1.985L) w =  3.0L. atm

NMSI #2: Energy/Work Practice Calculate the work associated with the expansion of gas from 46 L to 64 L at a constant external pressure of 15 atm.

NMSI #3: Energy/Work With Practice A balloon is being inflated to its full extent by heating the air inside it. In the final stages of this process, the volume of the balloon changes from 4.00 X 10 6 L to 4.50 X 10 6 L by the addition of 1.3 X 10 8 J of energy as heat. Assuming that the balloon expands against a constant pressure of 1.0 atm, calculate change of energy for the process. (To convert between L. atm and J, use 1 L. atm = J)

AP 2/26 You need to turn in your vocabulary assignmentYou need to turn in your vocabulary assignment Pick up white board, a marker, and the paper from the side tablePick up white board, a marker, and the paper from the side table You will also need a calculator, your AP thermo notes, something to write with, and YOUR AP formula chart, AND YOUR BRAIN AGAIN.You will also need a calculator, your AP thermo notes, something to write with, and YOUR AP formula chart, AND YOUR BRAIN AGAIN. Take out a piece of paper and number it 1-10Take out a piece of paper and number it 1-10 We will continue with thermo today by learning to calculate problems with CalorimetryWe will continue with thermo today by learning to calculate problems with Calorimetry HW for the weekend: The paper from the side table (it was suppose to have a back but it didn’t print off)HW for the weekend: The paper from the side table (it was suppose to have a back but it didn’t print off) Read over the thermo notes in the 5 steps to a five. Focus on calorimetry and understanding what a bomb and coffee cup calorimeter is.Read over the thermo notes in the 5 steps to a five. Focus on calorimetry and understanding what a bomb and coffee cup calorimeter is.

Energy Change in Chemical Processes Endothermic: Reactions in which energy flows into the system as the reaction proceeds. + q system - q surroundings

Endothermic- reaction which absorbs heat energy flows into the system thermal energy is changed into potential energy products have higher PE than reactants 2C + 2H kJ  C 2 H 4 2C + 2H 2  C 2 H 4 ΔH = 52.3 kJ/mol rxn Heat term is on the left side of the equation. For an endothermic reaction, the ΔH is POSITIVE! OR

Energy Change in Chemical Processes Exothermic: Reactions in which energy flows out of the system as the reaction proceeds. - q system + q surroundings

Exothermic- reaction which releases heat energy flows out of the system potential energy is changed to thermal energy products have lower potential energy than reactants OR 2C 8 H O 2  16CO H 2 O ΔH=  5076 kJ/mol rxn 2C 8 H O 2  16CO H 2 O kJ Heat term is on the right side of the equation. For an exothermic reaction, ΔH is negative.

Enthalpy (flow of heat in a system) can be calculated by: Stoichiometry Calorimetry From tables of standard values (heat of formation) Hess’s Law (Big Momma Equation) Bond Energies

NMSI #4: Enthalpy/Stoichiometry Upon adding solid potassium hydroxide pellets to water the following reaction takes place: KOH (s)  KOH (aq) + 43 kJ/mol Answer the following questions regarding the addition of 14.0 g of KOH to water: Does the beaker get warmer or colder? IS the reaction endothermic or exothemic? What is the enthalpy change for dissolution of the 14.0 grams of KOH?

Example ~ Enthalpy: For the reaction 2Na + 2H 2 O  2NaOH + H 2,  H =  368 kJ/mol rxn Calculate the heat change that occurs when 3.5 g of Na reacts with excess water. 3.5g Na 1 mol Na 368 kJ = 23.0g Na 2 mol Na  H =  28 kJ (or 28 kJ is released)

Calorimetry ( one way to determine heat change) calorimeter The amount of heat absorbed or released during a physical or chemical change can be measured, usually by the change in temperature of a known quantity of water in a calorimeter.

Calorimetry can be used to find the ΔH for a chemical reaction, the heat involved in a physical change, or the specific heat of a substance.

Units for Measuring Heat Joule The Joule is the SI system unit for measuring heat: calorie The calorie is the heat required to raise the temperature of 1 gram of water by 1 Celsius degree

Calculations Involving Specific Heat C = Specific Heat Capacity q = Heat lost or gained  T = Temperature change q = mC  T

Specific Heat The amount of heat required to raise the temperature of one gram of substance by one degree Celsius.

Definitions related to calorimetry: 1. q: is the quantity of heat absorbed or released during a chemical or physical change AND is proportional to the change in temperature1. q: is the quantity of heat absorbed or released during a chemical or physical change AND is proportional to the change in temperature 2. heat capacity- quantity of heat needed to change the temperature 1K of a system2. heat capacity- quantity of heat needed to change the temperature 1K of a system 3. specific heat capacity- quantity of heat needed to raise temperature 1 gram of a substance 1 K3. specific heat capacity- quantity of heat needed to raise temperature 1 gram of a substance 1 K 4. molar heat capacity- amount of heat needed to change temperature of 1 mole of a substance by 1 K4. molar heat capacity- amount of heat needed to change temperature of 1 mole of a substance by 1 K 5. Calorimeter- instrument used to measure heat change of system (two types: coffee cup calorimeter and bomb calorimeter)5. Calorimeter- instrument used to measure heat change of system (two types: coffee cup calorimeter and bomb calorimeter)

Calorimetry Practice # What is the specific heat of aluminum if the temperature of a 28.4 g sample of aluminum is increased by 8.1 o C when 207 J of heat is added?

Calorimetry Practice # What is the specific heat of silicon if the temperature of a 4.11 g sample of silicon is increased by 3.8 o C when 11.1 J of heat is added?

Calorimetry Practice # When a 25.7 g sample of NaI dissolves in 80.0 g of water in a calorimeter, the temperature rises from 20.5 o C to 24.4 o C. Calculate  H for the process.

Calorimetry # A 2.50 g sample of zinc is heated, then placed in a calorimeter containing 65.0 g of water. Temperature of water increases from o C to o C. The specific heat of zinc is J/g o C. What was the initial temperature of the zinc metal sample? (final temperatures of zinc and water are the same)

Example: A coffee cup calorimeter contains 150 g H 2 O at 24.6 o C. A 110 g block of molybdenum is heated to 100 o C and then placed in the water in the calorimeter. The contents of the calorimeter come to a temperature of 28.0 o C. What is the heat capacity per g of molybdenum? q = mC  T q = 150g(4.18J/g o C)3.4 o C = 2132J 2132J = 110g (C)(72 o C) C = 0.27J/g o C Drawing pictures may help to answer the question.

Example: 4.00g of ammonium nitrate are added to mL of water in a polystyrene cup. The water in the cup is initially at a temperature of 22.5°C and decreases to a temperature of 19.3°C. Determine the heat of solution of ammonium nitrate in kJ/mol. Assume that the heat absorbed or released by the calorimeter is negligible. q = mC  T q = 104g(4.18J/g o C)3.2 o C = 1391J absorbed = 1.39 kJ 4.00g NH 4 NO 3 x 1 mol NH 4 NO 3 = mol 80.06g NH 4 NO kJ/ = 28 kJ/mol Drawing pictures may help to answer the question.

NMSI #5: Enthalpy/Calorimetry In a coffee cup calorimeter, mL of 1.0 NaOH and mL of 1.0 M HCl are mixed. Both solutions were originally at 24.6 o C. After the reaction, the final temperature is 31.3 o C. Assuming that all solutions have a density of 1.0 g/cm 3 and a specific heat capacity of J/g o C, calculate the enthalpy change for the neutralization of HCl by NaOH. Asssume that no heat is lost to the surroundings or the calorimeter.

NMSI #6: Enthalpy When 1 mole of methane (CH 4 ) is burned at constant pressure, 890 kJ/mol of energy is released as heat. Calculate change of H for a process in which a 5.8 gram sample of methane is burned at constant pressure.

NMSI #7: Calorimetry at Constant- Pressure When 1.00 L of 1.00 M barium nitrate solution is mixed with 1.00 L of 1.00 M sodium sulfate solution at 25 o C in a calorimeter, the white solid barium sulfate forms and the temperature of the mixture increases to 28.1 o C. Assuming that the calorimeter absorbs only a negligible quantity of heat, and that the specific heat capacity of the solution is 4.18 J/ o C. g, and that the density of the final solution is 1.0 g/mL, calculate the enthalpy change per mole of barium sulfate formed.