Problem 1 - Energy, q, w, Enthalpy, and Stoichiometry Consider the following rea

Question

Problem 1 - Energy, q, w, Enthalpy, and Stoichiometry Consider the following reaction: 2Mg(s)+O2(g)>>2MgO(s)?H = -1204kJ 1) Is this reaction exothermic or endothermic? 2) Calculate the amount of heat transferred when 2.5 g of Mg(s) reacts at constant pressure. Express your answer using two significant figures. 3)How many grams of MgO are produced during an enthalpy change of -97.0 kJ ? 4)How many kilojoules of heat are absorbed when 7.90 g of MgO(s) is decomposed into Mg(s) and O2(g) at constant pressure?

Explanation / Answer

2Mg(s) + O2(g) --> 2MgO(s)?H= -1203.6 kJ................. Mg(OH)2(s) --> MgO(s) +H2O(l) ?H= +37.1 kJ............ 2H2(g) +O2(g) -->2H2O(l) ?H= -571.7 kJ........... standard enthalpy (reaction) = the sum of the enthalpy (heat) of formation of products - the sum of the enthalpy (heat) of formation of reactants Ho(reaction) = Hof(products) - Hof(reactants) = -1203.6 -(37.1 -571.7 )= 669 KJ

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