Student will learn: 1. to read Phase diagrams 2. math calculations of energy for melting, freezing, vaporization, condensing or raising temperature of.
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Student will learn: 1. to read Phase diagrams 2. math calculations of energy for melting, freezing, vaporization, condensing or raising temperature of a compound or element. Thermal chemistry is study of the transfer of heat in chemical reactions and physical changes.
Thermal Chemistry Phase: any part of a system that has uniform composition and properties. ( solid, liquid, gas) Fluid: gas or liquid: a substance that can flow and take shape of the container. Diffuse: ability to mix with other liquids or gases (p.364 food coloring, perfume) Overhead
Vaporization: process - liquid or solid changes into a gas. “you have added energy and vaporized it” Evaporization: process - particles escape from the surface of a non boiling liquid and become gas. “naturally evaporated” Volatile liquids: liquids that evaporate readily “finger nail polish remover” Condensation: process which a gas becomes a liquid “ rain, water drops on out side of glass of cold drink” Boiling: conversion of a liquid to a gas within the liquid as well as the surface. Boiling Point: Temperature which vapor pressure of the liquid equals the atmospheric pressure.
Freezing or solidification: physical change of liquid to a solid by removal of heat or energy Freezing Point: Temperature which liquid and solid have same average kinetic energy. Melting: physical change of a solid to a liquid by the addition of energy. Melting point: the temperature at which a solid becomes a liquid. Sublimation: change of a solid directly to a gas. “CO 2.. Dry ice, Iodine, frost free freezer” Deposition: change of a gas directly to a solid. “ frost on grass or car windshield ”
Phase Diagrams graph which shows conditions of phase changes
Triple point = solid, liquid, gas coexist at equilibrium.
Critical Temperature point = cannot exist as a liquid regardless of pressure. The critical temperature point of water is 373.99 o c. Above this temperature, water cannot be liquefied, no matter how much pressure is applied.
Critical Pressure point = lowest pressure at which the substance can exist as liquid @ critical temp. The lowest pressure at which water can exist as a liquid is 217.75 atm @ the critical temperature point.
Describe all phase changes that would occur when heating the chemical from -80 o to 20 o at a constant pressure of 10atm. Phase Diagram At room temperature what is the phase of this chemical?
What are the phase changes at 16atm from -100 o to 40 o and their corresponding temperatures? Phase Diagram At room temperature what is the phase of this chemical?
Given a sample of this chemical, how would you phase change the liquid into a gas without changing the temperature? Phase Diagram Where is the triple point?Where is the critical point?
Thermal Chemistry study of transfer of heat in chemical reactions and physical changes. What is the difference? Temperature Heat Thermal energy
Temperature: measurement of motion… measurement of kinetic energy of the molecules …. Wood… …. cold (vs) hot water ……. Fever of 105 Normally use a thermometer Heat: The transfer of thermal energy. The energy that ‘flows’ from higher Temperature to lower temperature. … standing beside the burning wood and feeling the warmth… Thermal energy = total energy of matter… measured in joules… Q = thermal energy
Heat of Fusion: energy required to melt solid to a liquid Q = m H f Q = energy M = mass H f = heat of fusion Heat of Vaporization: energy required to vaporize a liquid Q = m H v Q = energy m = mass H v = heat of vapor “ look on your chemistry tables” Specific Heat = amount of energy required to raise 1gram of substance 1 degree of temperature. Q = m C p t “ look on your chemistry tables”
1.Calculate the amount of energy required to melt a small ice cube weighing 24 grams. 2. Calculate the amount of energy required to produce steam from 100 mL of water.
3. Find the molar heat of vaporization for a substance, given that 4.22 mol of the substance absorbs 32.8 kJ of energy when it changes from a liquid to a gas. 4. Aluminum is used in manufacturing Pepsi-cola cans. How much heat energy does the factory need to provide to melt the 3 grams of aluminum needed per can? The factory produces 3,000 cans per hour. How much energy is needed per hour? Aluminum’s melting point is 660 degrees Celsius.
Specific Heat = amount of energy required to raise 1gram of substance by 1 degree Q = m C p t Looking at the chart of specific heat…. Which requires the most heat to heat up? iron pipe or lead pipe Which requires least amount of heat to heat up? magnesium or gold Which requires least amount of heat to heat up? Fe, Zn, Ti
How much heat is needed to raise the temperature of a 20g aluminum Pepsi-cola can 35 degrees? 2.Calculate the heat lost from a 5g copper penny if cooled from 25 o c to 3 o c in the freezer.
3.Calculate the mass of water that uses 2508J of energy in raising its temperature from 80 o C to 100 o C. 4.Calculate the temperature rise if 224.25J of heat energy was added to a 30gram ice cube.
* HEATING CURVES VS COOLING CURVES HANDOUT CURVE SHEET
Heating-Cooling curve ( Enthalpy of Fusion and Vaporization label
Theory pt.1: The quantity of heat absorbed to melt a solid = the quantity of heat released to solidify the liquid.
Theory pt.2: The quantity of heat absorbed to vaporize a liquid = the quantity of heat released to condensate the vapor.
Theory pt.3: All solids absorb heat as they melt. This causes a phase change rather than a temperature change. Ex) ice melting: Temperature remains constant until all ice has melted….. The temperature of water will increase only after all ice has melted. Ex) boiling water.
Which segments on the curve represent constant temperature? What is the boiling point of this substance? How much energy is needed for vaporization? If this chart is based on 2 grams of substance how much energy is needed to melt 10 grams of the substance.
At what temperatures does phase changes occur? Which portion represents an decrease in heat absorbed and potential energy decreases while Kinetic energy remains constant? How much is the Heat of Vaporization? At what temperature is condensation?
What is the melting Temperature? How many minutes does this take to melt? What is the boiling point?
***Equilibrium*** Equilibrium: two opposing changes occur at equal rates Closed system: Matter can not enter or leave. “ but energy can” example: sunlight, heat from a burner, cooling by ice. Equilibrium equations: Whenever a liquid changes into a vapor it absorbs heat energy. liquid + heat energy vapor Whenever a vapor condenses, it gives off heat energy vapor liquid + heat energy Whenever a liquid, vapor reaches equilibrium liquid + heat energy vapor
Le Chatelier’s principle: When a system is at equilibrium and is disturbed by a stress it attains a new equilibrium that minimizes the stress. Stress is typically: temperature, concentration, pressure. Need to know: 2 nd Law of Thermodynamics Heat always travel from higher temp to lower temp. “ same with energy, voltage, concentration, pressure, etc…..everything” endothermic: absorbing energy or heat exothermic: releasing energy or heat
liquid + heat vapor Equilibrium and temperature p.374 Add extra heat…….shift toward vapor …. endothermic reaction Subtract heat (cool with ice) …shift toward liquid ….. exothermic reaction Equilibrium and Concentration p.375 Add extra liquid ….. Shift toward vapor Add extra vapor …. Shift toward liquid Equilibrium and Pressure p.376 Pressure exerted by a vapor with its corresponding liquid is called equilibrium vapor pressure Add heat …increase vapor which increases pressure vapor onto liquid. Subtract heat…decrease vapor which decreases pressure of vapor onto liquid. “ think of your pepsi-cola drinks” easier to keep carbonated when cold”