lecture6

18 jg c2000 g109 c 9112 j 9112 kj qrxn 9112

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Unformatted text preview: 470 g Mg reacts with 200.0 g HCl, ∆T = 10.9° C. Calculate ∆H for Mg + 2HCl Æ MgCl2 + H2 assume qrxn = -qwater and that acid acts like water qwater = sm∆T = (4.18 J/g °C)(200.0 g)(10.9° C) = 9112 J = 9.112 kJ qrxn = -9.112 kJ (reaction is exothermic, heat is lost) for 0.470 g Mg 0.470 g Mg x ∆H = 1 mol Mg = 0.0193 mol Mg 24.30 g Mg -9.112 kJ = -471 kJ 0.0193 mol Mg ∆H is an extensive property: it depends on the amount reacted (T is an intensive property) ∆H must be expressed in terms of amount reacted; usually in moles per balanced equation. A constant volume calorimeter (bomb calorimeter) is used to measure reactions in which large amounts of gas are formed. The sample is placed in a stainless steel bomb charged with combustible sample and excess oxygen, immersed in a tank of water. An ignition wire initiates the reaction, which causes a measured temperature change in the bomb and surrounding water. In the bomb calorimeter, ∆V is constant, so the q measured id qP, and ∆E...
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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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