Week 7.docx

# Week 7.docx - Written Assignment 7 Energy and...

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Written Assignment 7: Energy and Thermochemistry Answer all assigned questions and problems, and show all work. 1. Consider this reaction: 2CH 3 OH( l ) + 3O 2 ( g ) 4H 2 O( l ) + 2CO 2 ( g ) H = –1452.8 kJ/mol a. Is this reaction endothermic or exothermic? (2 points) i. Exothermic b. What is the value of ∆ H if the equation is multiplied throughout by 2? (2 points) i. -2905.6 c. What is the value of ∆ H if the direction of the reaction is reversed so that the products become the reactants and vice versa? (2 points) i. 1452.8 d. What is the value of ∆ H if water vapor instead of liquid water is formed as the product? (2 points) vape of water is 44.0 kj e. 4 of H20 liquid to solid = 176 kj f. -1452.8+176 = 1276 (Reference: Chang 6.24) 2. The first step in the industrial recovery of zinc from the zinc sulfide ore is roasting, that is, the conversion of ZnS to ZnO by heating: 2ZnS( s ) + 3O 2 ( g ) 3ZnO( s ) + 2SO 2 ( g ) H = –879 kJ/mol Calculate the heat evolved (in kJ) per gram of ZnS roasted. (5 points) a. Molar mass of ZnS= 97.46*2= 194.92 b. -879/194.92= -4.51 kj/g (Reference: Chang 6.25) 3. A 6.22 kg piece of copper metal is heated from 20.5 °C to 324.3 °C. Calculate the heat absorbed (in kilojoules) by the metal. Specific heat Cu = 0.385 J/g°C. (5 points) a. Q=MC^T b. Q= 6220*.385*(324.3-20.5) 1 Copyright © 2017 by Thomas Edison State University . All rights reserved.

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c. Q= 727509.86=727 KJ (Reference: Chang 6.33) 4. A sheet of gold weighing 10.0 g and at a temperature of 18.0 °C is placed flat on a sheet of iron weighing 20.0 g and at a temperature of 55.6
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• Spring '15
• Khurana

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