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Heat & Temperature Calculations
Chapter 6 Notes HEAT Heat & Temperature Calculations
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Temperature = a measure of the AVERAGE kinetic energy in the substance.
Celsius (°C) Fahrenheit (°F) Kelvin (°K)
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0°K = absolute zero = all molecular motion stops
NEED TO FIND FORMULA °F 1.8°C + 32 °C °F – 32/1.8 °K °C + 273 °K – 273 °K °C °F 0°K = absolute zero = all molecular motion stops
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H20 distilled water (pure water)
melting point = 0°C boiling point = 100°C
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Melting Points examples
Gallium a# 31 M.P. 86oF Iron a# M.P oF Mercury a# 80 M.P. -38oF Gold a# M.P oF Copper a# 29 M.P oF
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Boiling Points examples
Gallium a# B.P oF Iron a# B.P oF Mercury a# B.P oF Gold a# B.P oF Copper a# B.P oF
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Energy (heat) measure in Joules, BTUs (British Thermal Units) calories and Calories.
1 calories = Joules 1 BTU = 252 calories 1 Calorie = 1000 calories
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States of Matter Also called Phases of Matter Solids Liquids
Vapors (gases)
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Solids Have a definite shape Have a definite volume
Particles VIBRATE in place
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Liquids Have NO definite shape Have definite volume
particles SLIDE freely
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Gases (vapor) Have NO definite shape Have NO definite volume
particles fill the volume of the container
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Solids, Liquids & Gases Solids = can form crystals = solid where the particle are arranged into repeating patterns. Liquids = physical property of Viscosity = “thickness” – the resistance to flow. Gases = volume of gases depend greatly on pressure and temperature.
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Phase Changes Melting Freezing Vaporization Condensation Sublimation
physical changes
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Melting the process of changing from a solid to a liquid
energy is being put into the substance melting point = the temperature at which melting occurs – physical property the melting point of water is 0ºC
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Freezing the process of changing from a liquid to a solid
energy is being pulled out of the substance freezing point = same temperature as the melting point (used mainly in weather)
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Vaporization the process of changing from a liquid to a gas
energy in being put into the substance evaporation boiling
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Evaporation vaporization that occurs at the surface of the liquid
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Boiling vaporization that occurs throughout the liquid
boiling point = the temperature at which boiling occurs the boiling point of water is 100ºC
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Condensation the process of changing from a gas to a liquid
energy is being pulled out of the substance
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Sublimation the process of changing from a solid to a gas
energy is being put into the substance ex: dry ice (CO2)
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Heating of water heat of vaporization heat of fusion STEAM 100°C
WATER (liquid) heat of vaporization 0°C ICE heat of fusion
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Heat Transfer Conduction Convection Radiation
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Conduction transfer of heat by direct contact (molecule to molecule)
metals are good conductors poor conductors = insulators
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Convection transfer of heat by “convection currents” warm fluids are less dense than colder fluid thus warm fluids rise and cold fall. not possible in solids fluid = anything that flows (liquids & gases) hot air balloons, “convection” ovens
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Radiation transfer of heat by electromagnetic waves
some wavelengths of infrared & ultraviolet only type of transfer that can occur through empty space sun Earth
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Specific Heat The amount of heat needed to raise the temperature of one gram of a substance one degree Celsius.
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Factors in Specific Heat
types of substance (C) mass of the substance (m) how much of a temperature change (∆T) C = specific heat constant m = mass ∆T = difference in the temperature
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Specific Heat Calculations
∆Q = amount of heat absorbed (difference in the heat or heat change) ∆Q = m x ∆T x C The specific heat of water = 1.0 cal/g°C or = 4.2 joules/ g°C
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EXAMPLE #1: How many calories are absorbed by a pot of water with a mass of 500 grams in order to raise the temperature from 20°C to 30°C? C = 1.0 cal/g°C m = 500 grams ∆T = 10°C (30-20) ∆Q = m x ∆T x C ∆Q = (500 g)(10°C)(1.0 cal/g°C) ∆Q = 5000 calories
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EXAMPLE #2: How many joules are absorbed by a pot of water with a mass of 500 grams in order to raise the temperature from 20°C to 30°C? ∆Q = m x ∆T x C ∆Q = (500 g)(10°C)(4.2 J/g°C) ∆Q = 21,000 Joules C = 4.2 J/g°C m = 500 grams ∆T = 10°C (30-20)
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Phase Changes Heat of fusion (Hf)
the heat energy needed to melt (or freeze) a substance. All heat being put into the substance goes to the melting process thus the temperature does not change while the substance is melting.
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Phase Changes Heat of vaporization (Hv)
the heat energy needed to boil (or condense) a substance. All heat being put into the substance goes to the boiling process thus the temperature does not change while the substance is boiling.
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Heat & Phase Changes Hf = mass x Hf constant
The heat of fusion of water = 340 J/g Hv = mass x Hv constant The heat of vaporization of water = 2300 J/g
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EXAMPLE: How many joules of heat are necessary to melt 500 g of ice?
Chf = 340 J/g m = 500 g H = Chf x m H = (340 J/g)(500 g) H = 170,000 J
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