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Energy and Heat
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Law of Conservation of Energy and Law of Conservation of Matter
Energy is never created nor destroyed, only transferred This is the same for matter! The amount of matter in the universe is fixed, so…
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Energy is… The ability to do work. Forms of energy: Kinetic energy Potential energy Chemical energy Mechanical energy Thermal energy
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Heat: The flow of energy due to a temperature difference. Preventing heat loss: Utilizing heat:
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Heat and Reactions Exothermic- Endothermic-
Is the rxn for a chemical cold pack endo/exo? Is the rxn for lighting a Bunsen burner endo/exo?
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Quantitative Practice
30.0 g of 25.0 °C H2O is mixed with 30.0 g of 100 °C water. Estimate which temperature the final temp. will be closest to (if any), and calculate the exact final temperature if no energy is lost to the surroundings (do this on blank next slide).
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Calculation Space IF masses of substance being mixed are equal, and substances are the same, Tf = Since substances are the same, they will lose/gain energy at the same rate
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But what if the two substances are different materials?
When combining materials composed of two different substances, You must take heat capacity (C or s) into account. Heat capacity = specific heat = C = s
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specific heat = heat capacity
The amount of energy that it takes to raise the T of a substance by 1 deg. celsius (units are: J/g°C or cal/g°C) Ex: Cwater = J/g°C Ciron = J/g°C Cgold = J/g°C
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Q = mCT Q = m = C = T =
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Determine the final temperature if 300
Determine the final temperature if J of energy is transferred to 20.5 g of water at an initial temperature of 33.5 C. The specific heat of water is J /g C Given: Find:
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For an isolated system (no matter or energy transferred to surroundings)
Qlost = -Qgained If you had the following information, how would you determine the heat capacity of an unknown metal? Know: Ti,metal= 94.0 °C mwater = 50.0 g Ti, water = 24.1 °C Cwater = J/g°C mmetal = g Tf = 26.5 °C
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Calculation Space
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CPb = J/g°C If 1.50 g of lead shot (Pb) at Ti,Pb= 25.0 °C is combined with 50.0 g of distilled water with TH2O =95.7 °C, what will the final temperature of the mixture be? Qgained = -Qlost Q = mCΔT
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