lecture6

When the reaction is ignited the temperature rises

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Unformatted text preview: = qP Example: A bomb calorimeter with a heat capacity of 476 J/K is charged with 0.5173 g of ethanol (C2H5OH) and excess O2 and immersed in a insulated tank containing 740 g of water. When the reaction is ignited, the temperature rises from 25.000° C to 29.289° C. Calculate ∆E for the reaction C2H5OH + 3 O2 Æ 2 CO2 + 3 H2 O heat released by the reaction = heat absorbed by the water and the bomb q = sm∆T + C∆T = (4.184 J/gK)(740 g)(4.289 K) + (476 J/K)(4.289 K) = 15.3 kJ 15.3kJ 46.07 g q(rxn) = x = -1,364 kJ 0.5173 g 1 mole 6-4 Chapter 6 Thermochemistry 6.3 Hess's Law Enthalpy is a function of state, so for a reaction A Æ B ∆H1 = HB - HA B Æ A ∆Hrev = HA - HB ∆Hrev = -∆Hfor ∆H is an extensive property (depends on amount) so for 2A Æ 2B, ∆H2 = 2∆H1 Hess’ Law: When a process is considered as a sequence of steps, the enthalpy change for the overall process is equal to the sum of the ∆H values for each individual step. C(graphite) + O2(g) Æ CO2(g) ∆H = -393.5 kJ C(diamond) + O2(g) Æ CO2(g) ∆H = -395.4 kJ Calculate ∆H for the reaction C(graphite) Æ C(diamond) C(graphite) + O2(g) Æ CO2(g) ∆H = -393.5 kJ CO2(g) Æ C(d...
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This note was uploaded on 04/05/2014 for the course CHEM 1211 taught by Professor Jackduff during the Spring '13 term at SPSU.

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