Practice Packet: Energy. Regents Chemistry: Dr. Shanzer. Practice Packet. Chapter 4: Energy.

Transcription

1 Regents Chemistry: Dr. Shanzer Practice Packet Chapter 4: Energy

2 Energy Objectives Define energy. Demonstrate the difference between endothermic and exothermic reactions in terms of energy. Describe how heat is transferred. Chemistry 200 Video Lesson 1 What is Energy? Energy is the ability to do work or produce heat 1.)Potential Energy positional/stored Chemical Potential Energy Energy stored in a substance because of it s composition (chemical bonds) 2.)Kinetic Energy - motion Three Forms of Energy 1. Chemical 2. Thermal 3. electromagnetic Chemical Reactions & Energy Some reactions release energy (i.e. Combustion of propane) o These are called Exothermic reactions o Freezing of water Some reactions absorb/require energy (i.e. photosynthesis) o These are called Endothermic Reactions o Boiling of water Exothermic Reactions

3 Potassium Permanganate and Glycerine Barium hydroxide and Ammonium chloride Endothermic Reactions Heat Transfer Heat can only be measured when it is transferred from one piece of matter to another. o Calorimeter tool that measures heat (units Joules) Calorimeter Tool used to measure heat transfer

4 Temperature vs. Heat Chemistry 200 Video Lesson 2 Objective: How are temperature & heat different? How do we convert between Celsius & Kelvin? I. Heat A. the transfer of energy from a body of high temp. to a body of low temp. B. Unit - - > calories or joules II. Temperature A. the measure of average K.E. of the particles in a substance. (how hot or cold it is) B. Units are in Celsius ( C) or in Kelvin (K) III. Heat vs. Temperature How is Heat different than Temperature? ex: What is the temp. of 1000g ice? 0 C 1g ice? 0 C What would require more energy to be melted, 1000g ice or 1g ice? III. Kelvin A. K = C ex 1 : 35 C = K K = 35 C = 308K ex 2 : 225K = C C = K = - 48 C

5 B. Absolute Zero C or 0 K 1. Freezing point of H 2 O = 0 C, molecules are still moving slowly(vibrating) & still have K.E. 2. At absolute zero, the molecules have no K.E. NO MOVEMENT AT ALL!!

6 Specific Heat Capacity Objective: How do we calculate energy gained or lost using specific heat capacity? Chemistry 200 Video Lesson 3 I. Specific Heat Capacity (of a substance) A. amount of heat required to raise 1g of that substance 1 C B. different substances have different composition, therefore each have a different specific heat **specific heat of H 2 O = 4.18J/g C or J/g K** (REFERENCE TABLE B) II. Calculating Heat To determine heat absorbed or released in a reaction, we use the following formula: q = mc T q = heat(in Joules) m = mass of the substance C = specific heat of the substance (if H 2 O, look to Ref. Table B) T = Temp initial - Temp final (will always be +) ex 1 : How many Joules are absorbed when 50.0g of H 2 O are heated from 30.2 C to 58.6 C? q =? **(Identify known & unknown values always!!! Remember UNITS and SIG FIGS!!!!)** m = 50.0g C H2O = 4.18J/g C (Ref. Table B) T = 58.6 C C q = mc T q = (50.0g)(4.18 J )(28.4 C) g C q = J q = 5940 J (SIG FIGS) = 28.4 C

7 ex 2 : When 25.0g of H 2 O are cooled from 20.0 C to 10.0 C, what is the number of Joules of heat energy released? **(Identify known & unknown values always!!! Remember UNITS and SIG FIGS!!!!)** q =? m = 25.0g C H2O = 4.18J/g C (Ref. Table B) T = 20.0 C C = 10.0 C q = mc T q = (25.0g)(4.18 J )(10.0 C) g C q = 1045J q = 1050J (SIG FIGS)

8 Heat of Fusion Objective: How do we use heat of fusion (H F ) to calculate the energy required to melt or freeze a substance? Chemistry 200 Video Lesson 4 Heat of Fusion (melting) - the amount of heat energy per unit mass needed to convert a solid to liquid (fusion) or released in liquid to a solid (freezing) q = mh F q = heat (in Joules) m = mass of substance H F = heat of fusion = 334J/g Ref. Table B :) **How come H F only has J/g & specific heat of H 2 O (4.18J/g C) also has C or K?** ex 1 : How much heat energy is needed to melt 5.76g of ice at its melting point? **(Identify known & unknown values always!!! Remember UNITS and SIG FIGS!!!!)** q =? q=mh F m = 5.76g q= (5.76g)(334 J ) g H F = 334J/g q = J q = 1920 J (SIG FIGS) ex 2 : If 20.0g of a substance are completely melted at its melting point & 3444J are absorbed, what is the heat of fusion (H F ) of this substance? **(Identify known & unknown values always!!! Remember UNITS and SIG FIGS!!!!)** q = 3444J q=mh F 3444J = 20.0g(H m = 20.0g F ) 3444J H F =? = H F 20.0g H F = 172.2J/g H F = 172J/g (Sig Figs)

9 Heat of Vaporization Video Lesson 5 Objectives Use the heat of vaporization (H v ) to calculate the energy required to vaporize or condense a substance. Heat of Vaporization Vaporization o Phase change Liquid to vapor (gas) Amount of heat needed to convert a liquid into a gas at constant pressure and temperature (or condense a gas to liquid) TABLE s B & T (constants for water) o q = mh v Heat taken away Heat added Same amount of Heat H vw = 2260 J/g Example #1 How much heat is required to vaporize 15.0 grams of water at C? q = mh v H fw = 334 J/g q = (15.0 g)(2260 J/g) q = J

10 Example #2 How much energy is required to vaporize grams of water at its boiling point? q = mh v q = (10.0 g)(2260 J/g) q = J

11 Video Lesson 1: Energy Definition Characteristics/Facts Examples Exothermic Non- examples Definition Characteristics/Facts Examples Endothermic Non- examples

12 Heat Transfer All substances are made up of small particles, which can be atoms or molecules that are constantly moving. The faster the molecules are moving, the more energy they have. The total energy of motion in the particles of a substance is called thermal energy. Temperature is the average amount of energy of motion in each particle of a substance. It is a measure of how hot or cold a substance is. A thermometer is a thin glass tube with a bulb on one end that contains a liquid, usually mercury or colored alcohol. Thermometers work because liquids expand when they are heated and contract when they are cooled. Temperature is measured in units called degrees. On the Celsius scale, the freezing point of pure water is 0 C and the boiling point of pure water is 100 C. On the Kelvin scale, the freezing point of pure water is 273 K and the boiling point is 373 K. 1. The Latin word calor means heat, and meter comes from the Greek word meaning to measure. What do you think a calorimeter does? 2. Where have you heard the word calorie before? What do you think a calorie is? A calorimeter is an insulated container filled with a liquid, usually water. When a hot object is placed in the calorimeter, heat energy is transferred from the object to the water and the water heats up. The temperature change of the water is recorded and by using a simple math equation, the amount of heat transferred can be calculated. A piece of gold at C is placed in a simple calorimeter. The starting temperature of the water is 30 0 C. 1. Draw an arrow on the diagram to represent the direction of heat flow. 2. The temperature of the water will increase or decrease? 3. Name the 3 forms of energy

13 Exothermic and endothermic reactions Decide whether each of these reactions is exothermic or endothermic: a) When two chemicals mix their temperature rises: b) A solid burns brightly and releases heat, light and sound: c) When two chemicals are mixed their temperature drops: d) Two chemicals will only react if you heat them continually: e) Plants take in light energy for photosynthesis: Multiple Choice 1. What occurs when 35- gram aluminum cube at 100 o C is placed in 90. Grams of water at 25 O C in an insulated cup? 1) Heat is transferred from the aluminum to the water and the temperature of the water decreases. 2) Heat is transferred from the aluminum to the water and the temperature of the water increases. 3) Heat is transferred from the water to the aluminum and the temperature of the water decreases. 4) Heat is transferred from the water to the aluminum and the temperature of the water increases. 2. Which type of energy is associated with the random motion of particles in a sample of gas? 1) Chemical energy 3) Nuclear energy 2) Electromagnetic energy 4) Thermal energy 3. Given the balanced equation representing a reaction: 2H2O (l) + energy! 2H2 (g) + O2 (g) What occurs as a result of this reaction? 1) The reaction is exothermic and energy was absorbed 2) The reaction is exothermic and energy was release 3) The reaction is endothermic and energy was absorbed 4) The reaction is endothermic and energy was released 4. Which unit is used to express the energy absorbed or released during a chemical reaction? 1) Kelvin 3) Volt 2) Joule 4) Torr

14 5. Which phase change is exothermic? 1) H2O (s)! H2O (g) 2) CO2 (s)! CO2 (l) 3) H2S (g)! H2S (l) 4) NH3 (l)! NH3 (g) 6. Which of these processes is always exothermic? 1) evaporation 3) combustion 2) insulation 4) Melting 7. When ammonium chloride dissolves in water the temperature falls. The type of energy change is described as? 1) exothermic 3) endothermic 2) activated 4) a decomposition 8. The chemical change when a fuel burns can be described as? 1) precipitation 3) a reversible reaction 2) an exothermic reaction 4) an endothermic reaction Video Lesson 2: Heat vs. Temperature Convert the following temperatures to Celsius ( C) or Kelvin (K) ºC à K K à C ºC à K ºC à K K à C 6. 0 K à C 7. 23ºC à K ºC à K ºC à K K à C x 10 2 K à C K à C Multiple Choice 1. Which statement defines the temperature of a sample of matter? 1) Temperature is the measure of the total electromagnetic energy of the particles. 2) Temperature is the measure of the total thermal energy of the particles. 3) Temperature is the measure of the average potential energy of the particles. 4) Temperature is the measure of the average kinetic energy of the particles. 2. At which temperature would atoms of a He(g) sample have the greatest average kinetic energy? 1) 25 C 3) 273 K 2) 37 C 4) 298 K

15 3. The average kinetic energy of water molecules increases when 1. H2O (s) changes to H2O(l) at 0 C 2. H2O(l) changes to H2O(s) at 0 C 3. H2O(l) at 10 C changes to H2O(l) at 20 C 4. H2O(l) at 20 C changes to H2O(l) at 10 C 4. Which graph best shows the relationship between Kelvin temperature and average kinetic energy? 5. At which temperature would the molecules of a one gram sample of water have the lowest average kinetic energy? 1. 5 C 3. 5 K C K Video Lesson 3: Specific Heat Capacity 1. How many Joules are absorbed when 4.0 g of H2O is heated from 12 C to 39 C? 2. A sample of H2O at 17 C has 250 Joules of heat added. The temperature then rises to 33 C. What is the mass of the H2O sample?

16 3. How many Joules of energy is required to heat 12g of H2O from 24 C to 52 C? Also calculate how many kilojoules? Joules is added to 12.0g of H2O at 16 C. What is the final temperature of the H2O sample? 5. An unknown sample of metal has a mass of 24.5g. The addition of 350 Joules causes the metal sample to increase in temperature by 12 C. Calculate the specific heat capacity of the unknown metal. 6. A 12.4g sample of H2O has 300 Joules of heat energy removed. If the final temperature of the H2O was 12 C, what was the initial temperature of the H2O? Video Lesson 4: Heat of Fusion 1. How much heat is needed to melt 35.0 g of ice at 0 ºC? Express your answer in kilojoules. 2. Calculate the heat energy required in joules, to melt 5.00 x 10 2 grams of ice at 0.0 C.

17 3. How many Joules of heat is required to melt 42g of ice at 0 C to H2O at the same temperature? 4. What is the mass of water that releases 65,247 J when it freezes? 5. Calculate the heat of fusion for a substance that requires 1253 joules to melt and has a mass of 19.9 g. Is this substance water? Explain. Video Lesson 5: Heat of Vaporization 1. How much energy is required to vaporize grams of water at its boiling point? 2. The heat of vaporization of a liquid is 1,340 J/g. What is the minimum number of Joules needed to change 45.0 grams of liquid vapor at the boiling point? 3. What is the total number of kilojoules required to completely boil g of water at C? 4. At 1 atm of pressure, 25.0 g of a compound at its normal boiling point are converted to a gas by the addition of 34,400 J. What is the heat of vaporization for this compound? 5. How many joules of energy are required to vaporize 423g of water at 100 o C and 1 atm?

18 Using the Heat Formulas 1. A gram sample of water is heated so that its temperature increases from 10.0 o C to 15.0 o C. What is the total amount of energy absorbed by the water? 2. When 20.0 grams of a substance are completely melted at its melting point, 3444J are absorbed. What is the heat of fusion for this substance? 3. What would be the temperature change if 3.0 gram of water absorbed 15 Joules of heat? 4. What is the specific heat of silver if a 93.9 g sample cools form C to C with the loss of 428 J of energy? 5. What is the number of kilojoules of heat needed to change 15 g of ice to water a 0 o C? 6. In question 5, is heat being absorbed or released? Is this process endothermic or exothermic? 7. What is the total number of kilojoules required to completely boil g of water at C?

19 8. If J are added to 20.0 g of water at 30.0 o C, what will be the final temperature of the water? 9. At 1 atm of pressure, 25.0 g of a compound at its normal boiling point are converted to a gas by the addition of 34,400 J. What is the heat of vaporization for this compound? 10. The temperature of a sample of water in the liquid phase is raised 30.0 o C by the addition of 3762 J. What is the mass of the water?