c161l16_10_09

# c161l16_10_09 - W To express the energetics associated with...

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Heat Transfers Heat Transfers W Heat capacity - the amount of energy it takes to cause a temperature change in a system change e temperatur absorbed heat C = W Specific heat capacity - the heat capacity per gram of system C = m × s

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W q = C Δ T W q = ms Δ T W The temperatures do not have to be converted to kelvin. Why? Example: starting temp. 10 °C, ending temp. 20 °C Δ T = 10 °C starting temp. 283K, ending temp. 293K Δ T = 10K
Heat measurement in Heat measurement in calorimeter calorimeter System Surroundings

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Example Example W An alloy of mass 25.0g was heated to 88.6 °C and then placed in a calorimeter that contained 61.2g of water at 19.6 °C. The temperature of the water rose to 21.3 °C. What is the specific heat capacity of the alloy? W Step 1: Heat gained = heat lost T s m T s m water water metal metal Δ = Δ 25.0g × s × (88.6-21.3)K=61.2g×4.184J K -1 g -1 ×(21.3-19.6)K s = 0.259 J g -1 K -1
Enthalpies of Reaction Enthalpies of Reaction W Remember our goal of discussing thermochemistry?

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Unformatted text preview: W To express the energetics associated with chemical reactions W Enthalpy is an extensive property The amount reacting changes the amount of heat released Thermochemical Thermochemical equations equations W Equation showing what reacts how much reacts how much energy is involved W CH 4 (g) + 2O 2 (g) CO 2 (g) + 2H 2 O(l) H = -890kJ Enthalpy as a state function Enthalpy as a state function W If we double the amounts, we double the energy W 2CH 4 (g)+4O 2 (g) 2CO 2 (g)+4H 2 O(l) H=-1780kJ W Since enthalpy is a state function, if you reverse the reaction, you reverse the sign W CO 2 (g) + 2H 2 O(l) CH 4 (g) + 2O 2 (g) H=+890kJ Energy calculations Energy calculations W Thermochemical equations relate the number of moles used or produced in a reaction to the energy produced or consumed. W We can treat the enthalpy the same way we treat reactants or products....
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## This note was uploaded on 11/12/2011 for the course CHEM 160:161 taught by Professor Siegel during the Fall '09 term at Rutgers.

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c161l16_10_09 - W To express the energetics associated with...

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