Unit 6 Review Kinetics and Thermochemistry

Wednesday 5/4 Have phase diagram hw out right away please Wednesday 5/4 Have phase diagram hw out right away please AFTER SCHOOL REVIEW WILL BE AWESOME! IT IS ALSO ON THE WEB FOR THOSE OF YOU WHO CAN’T MAKE IT. PLEASE COME! 2:20 – 3:15. 5 EXTRA CREDIT POINTS. AND EXTENSION ON LAST NIGHTS HW.

Unit 6 Review Kinetics and Thermochemistry Please take out paper to complete today’s review. Your notes may also be helpful. Each part of today’s in class review is worth points. Please number each slide and complete each section. You will have a limited amount of time for each section. Please keep up.

1 - Specific Heat What mass of magnesium is present if 250 J raises the temperature from 25 °C to 27 °C? Specific heat 1.02 J/gK What is the heat capacity of an unknown metal if 65.5 grams absorbs 1550 J and undergoes a temperature change of 62.0 C°?

1 - Specific Heat Answers What mass of magnesium is present if 250 J raises the temperature from 25 °C to 27 °C? Specific heat 1.02 J/g °C ◦ m= 250 J/(1.02 J/g °C x 2 °C) = g = 120 g What is the heat capacity of an unknown metal if 65.5 grams absorbs 1550 J and undergoes a temperature change of 62.0 C°? ◦ Cp = 1550J / (65.5 g x 62.0 °C) = J/g °C

2 - Calculation of Energy How many joules are required to melt 650 grams of water? How many joules are required to boil 650 grams of water? Substance Specific Heat (J/g ◦ C) H2O (l) H2O (steam) 2.02 Water Heat of fusion = 334 J/g Heat of vaporization = 2260 J/g

2 - Calculation of Energy Answers How many joules are required to melt 650 grams of water? ◦ H fusion = 334 J/g x 650 g = 217,100 J = 220,000 J How many joules are required to boil 650 grams of water? ◦ H vap = 2260 J/g x 650 g = 1,469,000 J = 1,500,000J Substance Specific Heat (J/g ◦ C) H2O (l) H2O (steam) 2.02 Water Heat of fusion = 334 J/g Heat of vaporization = 2260 J/g

3- Heat Curve… 1.Going from a solid to a gas is an (exothermic, endothermic) process because energy is (absorbed, released). 2. During phase changes the temperature (increases, decreases, remains constant). 3. List the states of matter in order of increasing kinetic energy. 4. Why does sweating help cool you off?

3- Heat Curve Answers 1.Going from a solid to a gas is an (exothermic, endothermic) process because energy is (absorbed, released). 2. During phase changes the temperature (increases, decreases, remains constant). 3. List the states of matter in order of increasing kinetic energy. Solid to liquid to gas 4. Why does sweating help cool you off? Sweating happens when water molecules evaporate (vaporize) from liquid droplets on your arm to gas. When these high energy molecules escape they lower the overall kinetic energy of the remaining molecules – lowering your body temperature as a result!

4- Phase Change Diagrams Which line represents the freezing point? Which line represents the boiling point? Describe what happens a the triple point? Describe what happens at the critical point?

4 - Phase Change Diagrams Answers Which line represents the freezing point? (fusion line) Which line represents the boiling point? (vaporization line) Describe what happens a the triple point? (all 3 states exist simultaneously) Describe what happens at the critical point? (the liquid state can no longer exist at these extremely high temps – no matter the pressure)

5 - Phase Change Diagram 1. How could you directly change “Q” to a solid? 2. Identify two ways you could change “Q” to a gas. Be specific. 3. Describe CLEARLY what is happening when A becomes A’. 4. Describe CLEARLY what is happening when B becomes B’. Q

5 - Phase Change Diagram Answers 1. How could you directly change “Q” to a solid? 2. Decrease temp at same pressure. 3. Identify two ways you could change “Q” to a gas. Be specific. 4. Raise temp at same pressure. OR, lower pressure at same temp. 5. Describe CLEARLY what is happening when A becomes A’. 6. Pressure held constant. Solid A heated, solid A melts at MO, liquid A is heated, liquid A vaporizes at PO, gaseous A is heated to A’. 7. Describe CLEARLY what is happening when B becomes B’. 8. Pressure held constant. Solid B is heated, solid B sublimates at SO, gaseous B is heated to B’ Q

6 - Potential Energy Diagrams Draw an energy diagram: Heat of reactants: 4.5 KJ Heat of products:10.5 KJ Energy of activated complex: 15 KJ Heat of reaction: _____ KJ Activation Energy: ______ KJ Exothermic/Endothermic? How does a catalyst affect this graph?

6 - Potential Energy Diagrams Answers Draw an energy diagram: Heat of reactants: 4.5 KJ Heat of products:10.5 KJ Energy of activated complex: 15 KJ Heat of reaction: _____ KJ (10.5 – 4.5 = 6 KJ) Activation Energy: ______ KJ (15 – 4.5 = 10.5 KJ) Exothermic/Endothermic? ENDOTHERMIC (Products higher than reactants) How does a catalyst affect this graph? (lowers the activation energy so faster reaction)

7 - Potential Energy Diagrams Draw an energy diagram: Heat of reactants: 250 KJ Heat of products: 25 KJ Energy of activated complex: 350 KJ Heat of reaction: _____ KJ Activation Energy: ______ KJ Exothermic/Endothermic? How does a catalyst affect this graph?

7 - Potential Energy Diagrams Answers Draw an energy diagram: Heat of reactants: 250 KJ Heat of products: 25 KJ Energy of activated complex: 350 KJ Heat of reaction: _____ KJ(25 – 250 = -225 KJ) Activation Energy: ______ KJ (350 – 250 = 100 KJ) Exothermic/Endothermic? EXOTHERMIC, energy of products is LESS than reactants so excess energy given off! How does a catalyst affect this graph? Again, catalyst lowers the activation energy

8 - Collision Theory Identify 5 ways to increase the rate of a reaction.

8 - Collision Theory Answers Identify 5 ways to increase the rate of a reaction. Increase temp – more collisions Increase concentration of reactants – more collisions Increase Pressure Decrease volume Add a catalyst Add a more reactive substance

9- Reaction Rate Calculate the rate of the reaction below. Time (second)

9- Reaction Rate Answers Calculate the rate of the reaction below. Rate = change in something/change in time = (135 nm – 0 nm)/100 sec = 1.35 nm/sec Time (second)