Agenda 4/16/2013 Turn in Test Corrections Part 1 – Rates of Reaction Slip Quiz part 1 Objectives Study Guide – switch and grade – to turn in. Related Released Questions – correct your own – to keep to prepare for a quiz. Part 2

Slip-Quiz Part 1 1.H 2 (g) + Cl 2 (g) → 2 HCl(g) Which statement best describes the rate of this chemical reaction? a.An increase in the concentration of HCl and H 2 with time. b.An increase in the concentration of HCl with time. c.A decrease in the concentration of HCl with time. 2. Explain how increasing the amount of Cl 2 (g) in the reaction chamber (keeping volume constant) will affect the rate of the reaction above.

Slip-Quiz Part 1 1.H 2 (g) + Cl 2 (g) → 2 HCl(g) Which statement best describes the rate of this chemical reaction? b. An increase in the concentration of HCl with time. Increase in concentration of product with time. 2. Explain how increasing the amount of Cl 2 (g) in the reaction chamber (keeping volume constant) will affect the rate of the reaction above. Increasing the amount of Chlorine gas in a chamber will be like increasing the concentration of the gas(more molecules per unit volume) so the

Slip-Quiz Part 1 2. Explain how increasing the amount of Cl 2 (g) in the reaction chamber (keeping volume constant) will affect the rate of the reaction above. Increasing the amount of Chlorine gas in a chamber will be like increasing the concentration of the gas(more molecules per unit volume) so the chances of collisions occurring will increase and so the rate of the reaction is likely to increase.

Part 1 Objectives –Explain and describe reaction rates in terms of molecular motion (collision theory) –Relate rate of reaction to concentration, temperature, pressure and surface area –Measure rate of reaction in terms of decrease in concentration or reactants or the increase in concentration of products with time

Study Guide – switch & grade Write in corrections/ additions /40 (document camera)

Part 2 Objectives –Confirm that energy is absorbed when a material evaporates Relate that fact to material melting –Remember that energy is released when a material condenses (or freezes) –Solve problems involving heat flow using known values of latent heat of phase change

What’s going on? Find room temperature Period 2 21 °C K = 21°C = 294K Period °C K = 23.5°C = 296.5K

What’s going on? Beaker 100mL or 50 mL water – one covered, one uncovered. –Find room temperature, record –Find temperature of uncovered water, record –Remove temperature sensor and notice what happens to temperature – record. What’s going on? –Find temperature of covered water, record. Remove temperature sensor and notice what happens to temperature again.

What’s going on? Beaker 100mL or 50 mL water – one covered, one uncovered. –room temperature, 21°C (294K) –temperature of uncovered water, lower than room temperature °C As remove sensor from water temperature…. –temperature of covered water, lower than room but warmer than uncovered beaker °C. As remove sensor from water temperature…..

What’s going on? Beaker 100mL or 50 mL water – one covered, one uncovered. –room temperature, °C –temperature of uncovered water, °C As remove sensor from water temperature…. –temperature of covered water, °C. A dynamic equilibrium is set up where H 2 O (l) → H 2 O (g) and H 2 O (g) → H 2 O (l) Rate of forward and backward reaction go at same rate. No further change can be observed.

Changes of State (Phase) Molar enthalpy (heat) of vaporization ΔH vap is defined as the heat required to vaporize one mole of a liquid (endothermic process, ΔH vap will have a positive value) H 2 O (l) H 2 O (g) ΔH vap = 40.7kJ Molar enthalpy (heat) of fusion ΔH fus heat required to melt one mole of a solid H 2 O (s) H 2 O (l) ΔH fus = 6.01kJ 16.3 Thermochemical equation for change of state Heat energy comes from surroundings, System is absorbing the energy

Specific Heat One calorie, or J, is the amount of heat required to raise the temperature of one gram of pure water by one degree Celsius J/g °C is defined as the specific heat of water. Specific heat of any substance – the amount of heat required to raise the temperature of 1g of that substance by 1°C Different substances have their own specific heat values see table 16-2

Enthalpy and Enthalpy Changes Difficult to know the total energy or heat content of any substance (many factors involved, not all fully understood) But changes in energy can be measured - for example by using a calorimeter (p 497 Figure 16-5) Enthalpy (H) is defined as the heat content of a system at constant pressure and the change in enthalpy for a reaction is called the enthalpy (heat) of reaction ΔH rxn Find in your Notes 16.2 Here we are… Calor, Latin for heat - Calorie I need to know what Enthalpy of fusion and vaporization are

Heating Curve of Substance X Time (min) Temperature ( °C) I Segment I Segment II Segment III

Heating Curve for 180g Sample of Water Time (min) Temperature ( °C) 1 Segment IV Segment V

Thinking Critically For each of the 5 regions (segment) of the graph, indicate how the absorption of heat changes the energy (kinetic or potential) of the molecules of substance X.

16.1 Energy The Nature of Energy Energy is the ability to do work or produce heat Potential energy – due to composition or position of an object Kinetic Energy – energy of motion, directly related to constant random motion of molecules and proportional to Temperature Bookcase Book

Thinking Critically Region I. solid X is warming up. The temperature is rising and we can say that the molecules are moving more quickly, or the kinetic energy of the water molecules is increasing.

Region II Temperature remains at 5°C for 4 minutes as solid X is melting to the liquid phase. The temperature is not rising so the molecules are not increasing their kinetic energy, rather the potential energy of the X molecules is increasing as they absorb thermal energy and use that energy to make the transition from being held in a crystal lattice to having more freedom to move around in liquid phase. p. 503 Potential energy – due to composition or position

Region III. Temperature increases from 5°C to 55°C over 10 minutes as liquid X heats up. The temperature is rising so the molecules are increasing their kinetic energy in this region of the heating curve.

Region 4. Temperature remains at 55°C for 4 minutes as liquid X is boiling, and all the molecules are making the transition to the vapor phase. The temperature of the substance is not rising so the molecules are not increasing their kinetic energy. The potential energy of the molecules of X is increasing. The molecules absorb thermal energy and use that energy to make the transition from being in the liquid phase to having even more freedom to move around in space in the gas phase. Potential energy – due to composition or position

Changes of State (Phase) Molar enthalpy (heat) of vaporization ΔH vap is defined as the heat required to vaporize one mole of a liquid (endothermic process, ΔH vap will have a positive value) H 2 O (l) H 2 O (g) ΔH vap = 40.7kJ Molar enthalpy (heat) of fusion ΔH fus heat required to melt one mole of a solid H 2 O (s) H 2 O (l) ΔH fus = 6.01kJ Go to next section Notes 16.3 What do you notice about the size of the heat of vaporization value and the time it took to boil all the water sample vs. the heat of fusion and the time it took for the ice to melt?

Region V. Temperature increases from 55°C as the molecules are increasing their kinetic energy in this region of the heating curve – moving faster and faster in gaseous phase.

Thinking Critically cont. Region 4. T final = 100°C, Tinitial =100°C Can’t use q = cmΔT to find heat required, again this is a phase change need to use the Molar enthalpy (heat) of vaporization ΔH vap heat required to vaporize one mole of a liquid H 2 O (l) H 2 O (g) ΔH vap = 40.7 kJ/mol q= number moles x ΔH vap = 10 mol x 40.7kJ/mol = 410 kJ The more heat is required the longer the region will be on the graph. p. 503