Name: Regents Chemistry: Mr. Palermo Notes: Unit 7 Heat 1
Name: KEY IDEAS Heat is a transfer of energy (usually thermal energy) from a body of higher temperature to a body of lower temperature. Thermal energy is the energy associated with the random motion of atoms and molecules. (4.2a) Temperature is a measurement of the average kinetic energy of the particles in a sample of material. Temperature is not a form of energy. (4.2b) The concepts of potential and kinetic energy can be used to explain physical processes that include: fusion (melting), solidification (freezing), vaporization (boiling, evaporation), condensation, sublimation, and deposition. (4.2c) VOCABULARY For each word, provide a short but specific definition from YOUR OWN BRAIN! No boring textbook definitions. Write something to help you remember the word. Explain the word as if you were explaining it to an elementary school student. Give an example if you can. Don t use the words given in your definition! Potential Energy: Kinetic Energy: Heat: Specific Heat: Heat of Fusion: Heat of Vaporization: Endothermic: Exothermic: 2
Lesson 1: What is Heat? Objective: Determine the direction of heat flow Determine the change in heat of a reaction POTENTIAL ENERGY: Stored energy KINETIC ENERGY: Energy of motion TYPES OF ENERGY: WHAT IS HEAT? Energy of random motion of atoms/molecules in a sample of matter Heat moves from HOT objects to cold Measured in Joules (table D) In terms of heat flow what happens when an ice pack is placed on your skin? PRACTICE: In a laboratory, a student makes a solution by completely dissolving 80.0 grams of KNO3(s) in 100.0 grams of hot water. The resulting solution has a temperature of 60. C. The room temperature in the laboratory is 22 C. What is the direction of heat flow? 1
Lesson 1: What is Heat? TEMPERATURE: Measure of the of the particles in matter PRACTICE: In which sample of water do the molecules have the highest average kinetic energy? a) 20. ml at 100. C b) 40. ml at 80. C c) 60. ml at 60. C d) 80. ml at 40. C ENERGY CHANGES DURING REACTIONS reactions release heat (energy on right) Ex. A + B C + Energy reactions absorb heat (energy on left) Ex. A + B + energy C TABLE I: SHOWS ENERGY CHANGES FOR SPECIFIC REACTIONS ΔH change in heat of reaction +ΔH (heat is exothermic) - ΔH (heat is endothermic) 2
Lesson 1: What is Heat? EXAMPLE TABLE I: When C2H4 is formed, is heat released or absorbed? EXAMPLE TABLE I (reverse reaction): When C2H4 is broken down, is heat released or absorbed? PRACTICE: When C(s) + O2 (g) CO2 (g) is heat absorbed or released? CHECK YOUR UNDERSTANDING: When 2NO2 (g) N2 + 2O2 (g) is heat absorbed or released? 3
Lesson 2: Calculating Heat Objective: Calculate heat, specific heat mass and change in temperature of a reaction q is the symbol for heat (equal to ΔH) o Measured in joules or kilojoules o if q is positive, the heat is endo. o if q is negative, the heat is exo. CALCULATING HEAT OF REACTIONS The heat of a reaction is based on: o the mass of the substance o the temperature change it undergoes o specific heat. SPECIFIC HEAT: The heat needed to raise the temperature of one gram of a substance one degree Celsius. Specific heat of water: located on table B Formula on Table T: q = heat m = mass c = specific heat of substance ΔT = final temp initial temp CALCULATING HEAT 1
Lesson 2: Calculating Heat EXAMPLE: Solving for heat (q) How much heat is needed to raise the temperature of 500. g of water by 15 C? Step1: List the known variables m = 500. g C = 4.18 J /g C (from Table B) ΔT = 15 C Step 2: Determine the product q = mcδt q = (500. g)(4.18 J /g C)(15 C) q = 31,500 J = 32,000 J EXAMPLE: Solving for specific heat (c) The temperature of 95.4g of copper increases from 25 to 48 C and absorbed 849J. Calculate copper s specific heat. PRACTICE: How many joules of heat are absorbed when 50.0g of water are heated from 30.2 C to 58.6 C? 2
Lesson 2: Calculating Heat PRACTICE: How much heat is needed to raise the temperature of 25 g of water from 27 C to 47 C? CHECK YOUR UNDERSTANDING 1: How much heat is needed to raise the temperature of 100g of water 50 C? CHECK YOUR UNDERSTANDING 2: The temperature of aluminum increases from 30 to 38 C and absorbed 900J. Calculate the mass of aluminum used if the specific heat is 0.902 j/g K. 3
Lesson 3: Phase Changes and Heat Objective: Differentiate between endo and exothermic Identify a phase change as either endo or exothermic REVIEW OF SOLIDS, LIQUID, GASES SOLIDS: LIQUIDS: GASES: 1
Lesson 3: Phase Changes and Heat Solid STRONGEST force of attraction between particles Liquids MODERATE force of attraction between particles Gases WEAKEST force of attraction between particles PHASE CHANGES: Phase changes: ENDOthermic (s) + heat (l) + heat (s) + heat (l) (g) (l) Phase changes: EXOthermic (l) (g) (g) (s) + heat (l) + heat (s) + heat 2
Lesson 3: Phase Changes and Heat THERMOCHEMSITRY The study of energy changes that occur in chemical reactions. Kinetic energy refers to energy of motion. (Temperature) Potential Energy refers to stored energy PHASE CHANGE DIAGRAM 3
Lesson 4: Calculating Heat of Phase Changes Objective: Calculate heat of phase changes using q=mhf and q=mhv HEAT OF FUSION: Located on Table B Heat needed to Formula located table T: V HEAT OF VAPORIZATION: Located on Table B Heat needed to Formula located table T: V 1
Lesson 4: Calculating Heat of Phase Changes EFFECTS OF IMF S ON Hv & Hf If the IMF is strong, the heats of vaporization and fusion is high (high melting/boiling pt) EXAMPLE: (Heat of fusion) How many joules does it take to melt a 16 gram sample of water at 0 C? EXAMPLE: (Heat of vaporization) How many joules does it take to boil a 250. gram sample of water at 100 C? PRACTICE: How much heat is needed to melt ice at 0C if the sample weighs 255g? PRACTICE: Calculate the number of joules needed to vaporize 423g of H2O 2
Lesson 4: Calculating Heat of Phase Changes CHECK YOUR UNDERSTANDING 1: How many joules of energy are required to vaporize 423g of water at 100 C? CHECK YOUR UNDERSTANDING 2: What is the total number of joules of heat needed to change 30.0g of ice to water at 0 C? HEATING CURVE (HEAT ADDED OVER TIME) Vertical Parts: Temp inc Avg. Kinetic energy inc Potential energy remains the same Horizontal Parts (Plateaus): Temp remains the same Avg. Kinetic energy remains the same Potential increases COOLING CURVE (HEAT REMOVED OVER TIME) Vertical Parts: Temp dec Avg. Kinetic energy dec Potential energy remains the same Horizontal Parts (Plateaus): Temp remains the same Avg. Kinetic energy remains the same Potential decreases REMEMBER THE 3 P S Plateau Phase change Potential energy change **diagonal Parts: Temperature is changing.therefore kinetic energy is changing 3