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Published byLilian Henriksen Modified over 5 years ago
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Thermochemistry: The study of heat changes that occur during chemical reactions and physical changes of state
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Energy Energy – the ability to do work or produce heat
Exists in 2 forms: Kinetic energy – energy of motion Potential energy – energy at rest or energy of position Heat (q) = the energy that transfers from one object to another because of a temperature difference between them Heat always flows from a warmer object to a cooler object
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Energy Kinetic energy – in a chemical reaction temperature is the determining factor The higher the temperature…the faster the particles move…the higher the average kinetic energy Temperature is a measure of the average kinetic energy Kelvin scale: 0 K = -273 °C
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Law of Conservation of Energy
Law of Conservation of Energy – Energy is neither created nor destroyed
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Heat (q) Heat or energy can be in joules, calories, kilocalories, or kilojoules The SI unit is the joule 1 Cal = 1000 cal = 1 kcal 1 cal = J 1kcal = 4186J 1 J = cal
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Heat Capacity The amount of heat it takes to change an object’s temperature by 1ºC Depends on an object’s mass Ex. A cup of water has a greater heat capacity than a drop of water.
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Specific Heat (C) Specific Heat (C) – the amount of heat required to raise 1 gram of a substance by 1C Specific heat is an intensive property, and therefore does not depend on size Every substance has its own specific heat Ex. Water = 4.18 J/(g x ºC) Glass = 0.50 J/(g x ºC)
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Specific Heat Units for C = J / (g x ºC) (joules per gram degree Celsius) Equation for Specific Heat: C = q / (m Δ T) C = specific heat; q = heat; m = mass and ΔT = change in temperature This equation can be rearranged to solve for heat (q) q= CmΔT
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Specific Heat A 10.0 g sample of iron changes temperature from 25.0C to 50.4 C while releasing 114 joules of heat. Calculate the specific heat of iron.
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Example C= q/ (m∆T) C=114 J/ (10.0 g x 25.4°C) C = 0.45 J/g C
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Another example If the temperature of 34.4 g of ethanol increases from 25.0 C to 78.8 C how much heat will be absorbed if the specific heat of the ethanol is 2.44 J/g C
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Another example First, rearrange the specific heat formula to solve for heat q = CmT q = (2.44 J/g°C)(34.4g)(78.8°C - 25°C) q = J
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Yet another example 4.50 g of a gold nugget absorbs 276 J of heat. What is the final temperature of the gold if the initial temperature was 25.0 C & the specific heat of the gold is 0.129J/g C
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Yet another example C= q/ (m∆T); rearrange to find ∆T = q / (C x m)
∆T = 276 J / (.129 J/g°C x 4.50 g) T = C T = Tf-Ti = Tf-25 Tf = C
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