REVIEW 1.Write a formula for the freezing of water. 2.Write a formula for the boiling of water. 3.Write a formula for the condensing of water. 4.Write a formula for the sublimation of water. 5.Write a formula for the sublimation of dry ice (solid CO 2 ). H 2 O (l)  H 2 O (s) H 2 O (l)  H 2 O (g) H 2 O (g)  H 2 O (l) H 2 O (s)  H 2 O (g) CO 2 (s)  CO 2 (g) Allotropes Stp K-celsius Freezing/melting table S

Time (min) Temperature 0 C solid liquid gas melting/freezing boiling/condensing Heating Curve of Unknown Substance Melting_______________________________________________ Melting Point_______________________________________________ Freezing ___________________________________________ Boiling ____________ Boiling pt.__________ Condensing ____________________________________________ A BC D E F B to C solid  liquid : on the plateau C to B liquid  solid : on the plateau = freezing point (must be temperatures) For this = 50 0 C D to E gas to liquid E to D (Boiling is opposite D to E) Endothermic = absorbing energy Both liquid & solid phases are present = condensation pt. For this substance = ~ C

Time (min) Temperature 0 C solid liquid gas melting boiling KE PE KE PE KE Kinetic Energy_____________________________________________ Potential Energy ___________________________________________ Sublimation_______________________________________________ Energy changes during Phase Changes Energy of motion, changes on the slopes, particles move faster Stored energy, changes on the plateaus, as particles rearrange Not on this graph: solid to gas like dry ice CO 2 (s) opposite is deposition, gas to solid like frost on windows urves.html

Time (min) Temperature 0 C solid liquid gas melting boiling Heat of fusion Heat of vaporization A BC DE F Temperature _____________________________________________ ________________________________________________________ Heat_______________________________________________________ Heat of Fusion _______________________________________________ Heat of Vaporization___________________________________________ Specific Heat_________________________________________________ Heating Curve form of energy that is measured in joules amount of heat needed to melt 1 gram of a substance amount of heat needed to boil 1 gram of a substance The amount of heat needed to raise 1 gram of a substance 1 0 C A measure of the average kinetic energy of the particles Ex: the higher the temperature, the higher the kinetic energy

Time (min) Temperature 0 C Cooling of a Substance A BC D E F ________1. Which section of the graph represents the substance in the solid phase only? ________2. Which section of the graph represents the substance in the gas phase only? ________3. Which section of the graph represents the substance in the solid and liquid phase? ________4. Which section represents condensing of the substance? EF AB DE BC Is this graph exothermic or endothermic?

Time (min) Temperature 0 C Cooling of a Substance A BC D E F ________5. Which section would the molecules of the substance have the highest average kinetic energy? ________6. How long does it take the solid to freeze once it has reached the freezing point? ________7. How long does the substance exist as a liquid only? ________8. What is the melting point of this substance? ________9. What is the boiling point of this substance? A or >90 0 C ~5 min ~3 min 30 0 C 70 0 C gas condensing liquid freezing solid

q = m C ∆ T if temperature is changing q = m H f if substance is melting or freezing q = m H v if substance is boiling or condensing Problems: Either there’s a phase change or the temperature is changing 1.The heat of fusion of water is ________________ How much heat is needed to change 10. grams of ice to liquid water at the freezing point? q__________________________________________________ m__________________________________________________ C__________________________________________________ ∆ T ________________________________________________ Formulas on Reference Tables heat (joules) mass (grams) specific heat (joules / gram 0 C) change in temperature ( 0 C) 334 J/g q = m H f (10 g) (334 J/g) = 3340 Joules Significant figures 3300 Joules

2. The heat of vaporization of water is _____________ How much heat is needed to change 10. grams of liquid water to steam at the boiling point? 3. How many joules is needed to raise the temperature of 10.0 grams of water from to C? 2260 J/g q = m H v = (10. g ) (2260 J/g) = Joules q = m C ∆ T = (10. g)(4.18 J/g 0 C) (5 0 C) = 209 Joules J Sig figs would have to be in scientific notation = 2.1 x 10 2 J

USE q = mCΔT USE q = mH f if freezing or melting q = mH v if boiling or condensing

Practice Problems 1. How many joules does it take to warm 20. g of water from C to C? 2. How many joules does it take to melt 75 grams of ice at C? 3. How many joules does it take to boil 20. g of water into steam at C joules of heat is needed to change the temperature of a substance from C to C. Determine the mass of the sample. q = m C ∆ T q = m H f q = m H v q = m C ∆ T

Practice Problems 1. How many joules does it take to warm 20. g of water from C to C? 2. How many joules does it take to melt 75 grams of ice at C? 3. How many joules does it take to boil 20. g of water into steam at C joules of heat is needed to change the temperature of water from C to C. Determine the mass of the sample. q = m C ∆ T q = m H f q = m H v = 20 g (4.18J/g 0 C) 15 0 C = 1254 J or 1300 J = 75 g ( 334 J/g) = J or J = 20 g (2260 J/g) = J or J q = m C ∆ T 150 J = m (4.18 J/g 0 C) 30 0 C 1.2 g

5. How much heat is needed to change 40.0 g of water into steam at the boiling point? joules of heat were added to 20. g of water. What is the final temperature of the water if it started at C? 7. How many joules are released when 5.0 grams of water cools from 32 0 C to C grams of gold (Au) absorbed 268 joules. The temperature of the sample went up C. What is the specific heat of the gold? q = m C ∆ T q = m H v

5. How much heat is needed to change 40.0 g of water into steam at the boiling point? joules of heat were added to 20. g of water. What is the final temperature of the water if it started at C? 7. How many joules are released when 5.0 grams of water cools from 32 0 C to C grams of gold (Au) absorbed 268 joules. The temperature of the sample went up C. What is the specific heat of the gold? q = m C ∆ T q = m H v = 40 g (2260 J/g) = 90,400 J 5000 J = 20 g (4.18 J/g 0 C) ∆ T ∆ T = C = 60 0 C so = 90 0 C = 5 g (4.18 J/g 0 C) 12 0 C250.8 J = 250 J 268 J = (100 g)(C) (20 0 C).13 J/g 0 C

8. Why is someone burned more severely from steam at C than water at C (Remember that the steam will condense when it hits your hand)

When water goes from gas to liquid it is undergoing what is called a phase change. Phase changes require a lot more energy than just a temperature change. The energy required for water to go from a liquid to a gas is called the heat of vaporization. When steam (water in the gas phase) hits your skin, a lot of energy will be released as it condenses into a liquid, undergoing a phase change. This energy release causes a much worse burn than if the same amount of boiling water were to hit your skin where it would decrease in temperature (to your skins temperature) but would not have to go through a phase change. The loss of energy that is released from steam hitting your skin occurs quickly and in a small localized area, therefore causing damage to your cells.

q = m C ∆ T q = m H v q = m H f 1. How much heat is needed to raise the temperature of 50. grams of water from 25 to 65 ? 2. How much heat is needed to boil 25 g of water into steam at C ? 3. How much heat is needed to melt 75 g of ice at 0 0 C ?

q = m C ∆ T q = m H v q = m H f 1. How much heat is needed to raise the temperature of 50. grams of water from 25 0 to 65 0 C? 2. How much heat is needed to boil 25 g of water into steam at C ? 3. How much heat is needed to melt 75 g of ice at 0 0 C ? q = 50 (4.18) 40 0 = 8360 J = 8400 J q = 25 ( 2260 ) = J = J q = 75 (334) = J = J

q = m C ∆ T 4. If 6500 joules of heat is added to 55 g of water, how much would the temperature rise? 5. How much water do you have if 4500 joules is added to a sample of water and the temperature changed from 35 0 to 95 0 C? 6. How many kilojoules is 4600 joules? ________________ 7. How many joules are in 8.2 kilojoules? _______________

q = m C ∆ T 4. If 6500 joules of heat is added to 55 g of water, how much would the temperature rise? 5. How much water do you have if 4500 joules is added to a sample of water and the temperature changed from 35 0 to 95 0 C? 6. How many kilojoules is 4600 joules? ________________ 7. How many joules are in 8.2 kilojoules? _______________ 6500 = 55 (4.18) T = = 28 0 C kilo hecto deka base or standard 4.6 KJ 8200 J 4500 = m (4.18) 60 0 C = = 18 g

8. What is the heat of fusion if 25 grams of a substance needed 6400 joules to melt it? 9. What is the total number of kilojoules required to boil 100. g of water at C 10. The heat of fusion of a compound is 126 Joules per gram. What is the total number of joules of heat that must be absorbed by a 15.0 gram sample to change the compound from a solid to a liquid at its melting point? 11. In which of the following samples, do the particles have the highest average kinetic energy? 1) 50 g at 1002) 40 g at 253) 100 g at 504) 10 g at 10

8. What is the heat of fusion if 25 grams of a substance needed 6400 joules to melt it? 9. What is the total number of kilojoules required to boil 100. g of water at C 10. The heat of fusion of a compound is 126 Joules per gram. What is the total number of joules of heat that must be absorbed by a 15.0 gram sample to change the compound from a solid to a liquid at its melting point? 11. In which of the following samples, do the particles have the highest average kinetic energy? 1) 50 g at C 2) 40 g at 25 0 C 3) 100 g at 50 0 C 4) 10 g at 10 0 C 6400 = 25 (H f ) = 256 J/g or 260 J/g q = m H f q = 100. g (2260) = J = 226 KJ q = m H f q = m H v q = 15 ( 126 ) = 1890 J