Thermochemistry/phase changes review Station 1

Transcription

1 Thermochemistry/phase changes review Station 1 (Show all work) Answers are posted below to check yourself 1. Calculate the heat necessary to raise the temperature of 40.0 g of aluminum from 20.0 o C to 32.3 o C. (look on your reference sheet for the Specific Heat of Aluminum) 2. Heated bricks or blocks of iron were used long ago to warm beds. A 1.49 kg block of iron heated to 155 o C would release how many joules of heat as it is cooled to 22 o C? The specific heat of iron is. (look on your reference sheet) Answers: x 10 3 Joules x 10 4 J Station 2: Phase Changes Determine if the following reactions are endothermic or exothermic. (Remember if it absorbs energy you are endothermic, if it releases energy it is exothermic) Going up the heating curve S L G is absorbing Going down the heating curve G L S is releasing What is this process called: absorbing/releasing 1. Solid liquid 2. liquid gas 3. Solid gas 4. Gas liquid 5. Liquid solid 6. Gas solid 7. Forming ice crystals 8. Exploding a firecracker

2 Station 3: Heat and Energy 1. Which way does heat flow? a. From hot to cold b. From cold to hot c. It doesn t d. It will go from hot to cold to hot 2. Explain what the kinetic energy of molecules will do for the following scenarios: a. Water starts to boil (increase/decrease) b. Water starts to freeze (increase/decrease) 3. If I add the same amount of heat to two different objects, why would they have different temperatures? a) Some objects heat up faster than others; their specific heat is different. Like metal compared to water. b) All heat transfer is not exact. It s impossible to add the same amount of heat to two things. c) Objects have different mass. For example, if I add 10 Joules of heat to a swimming pool as opposed to 10 Joules of heat to a cup of water, the cup of water will have a higher temperature because there is less mass to heat up. d) Both and e) Both and 7. What occurs when energy is removed from a liquid vapor system in equilibrium? A. The amount of liquid increases. B. The amount of vapor increases. C. The amounts of liquid and vapor increase equally. D. The amounts of liquid and vapor decrease equally. 8. Which explains the relationship between heat energy and temperature? A. As heat energy increases and temperature increases, freezing occurs. B. As heat energy decreases and temperature remains constant, condensation occurs. C. As heat energy decreases and temperature remains constant, evaporation occurs. D. As heat energy increases and temperature decreases, melting occurs

3 Station 4: Physical and Chemical 3. Give me three examples of a physical change 4. Give three examples of a chemical change 5. Give three examples of a physical property 6. Give three examples of a chemical property

4 Station 5: Specific Heat and Phase Change Key Equations 1 cal = Joules 1. Using what you know about specific heat, explain why do metals heat up and cool down so quickly? 2. Put the following in order of lowest to highest specific heats: water, air, metal. 3. What determines whether an object has a high heat capacitance or a low heat capacitance? 4. Denise has 400 grams of hot tea on her desk. You measured its temperature in the morning to be 80ºC. When you checked again at lunch, it was only 42ºC. If the specific heat capacity of the tea is J/gºC, how much heat was transferred to the environment? 5.How much energy is needed to heat a 125 g sample of water from 20 C to 100 C? (Note: a change in temperature means that this is a specific heat problem)

5 Station 6: Heating Curves Image Source: Figure 1: This is the graph of the temperature of a solid substance as time passes. Heat is being added to the substance at a constant rate throughout the range of the graph. Use this figure to answer questions 4 through Using figure 1, why is the temperature of the solid not changing between 5 minutes and 9 minutes? 5. Using figure 1, why is the temperature not changing between point D and point E? 6. What is the name of these ranges when heat is added but is not increasing the temperature of the substance? 7. Label the parts of the Graph A E. Put a circle around the area on the graph that a vapor would be present. 8. Explain how you would find the melting point and boiling point of an unknown substance.

6 Station 7: Heat of Vaporization and Heat of Fusion 1. What is the equation for heat of fusion? 2. What is the equation for heat of vaporization? 3. If 2083 Joules are used to melt 5.26 grams of aluminum, what is the heat of fusion of aluminum? 4. If the same amount (5.26 g) of zinc is melted, it takes 579 Joules to completely melt the sample. What is the heat of fusion of zinc? 5. How much energy does it take to boil a 125 g sample of water? 6. How much energy does it take to heat 125 g of steam from 100 C to 110 C? (Specific heat of steam= 2.01 J/g C) Why does it require 5,511 J of heat energy to melt 16.5 g of ice? A. 2,260 J/g of heat energy is absorbed by the ice as it is converted from a solid to a liquid. B. 334 J/g of heat energy is absorbed by the ice as it is converted from a solid to a liquid. C J/g C of heat energy is required as ice is converted from a solid to a liquid. D J/g C of heat energy is required as ice is converted from a solid to a liquid.