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Unformatted text preview: ECH 152A, Fall 2011, Roland Faller Solutions for Homework 6, November 7, 2011 Problem 1 (a) Estimate Δ H ◦ f (298K) for the following at 25 ◦ C: Acetylene, n-Hexane, Styrene (b) Determine the standard heat of reaction for the following (25 ◦ C): N 2 (g)+3H 2 (g) → 2NH 3 (g); C 2 H 4 (g)+H 2 O(l) → C 2 H 5 OH(l) N 2 (g)+C 2 H 2 (g) → 2HCN(g) Solution (a) Estimation: Read the numbers of the table in the book, to obtain acetylene 225 kJ/mol, hexane -167 kJ/mol, styrene 147 kJ/mol. If we take the numbers right off the table we have to be aware that they may be for gas and not for liquid so we may need to correct with the enthalpy of vaporization. And that there is always some error, therefore estimation. (b) The heats of reaction are always the heats of formation of the products minus the heats of formation of the reactants taking into account the stoichiometric ratios Δ H ◦ reac (298K) = ∑ ν i Δ H ◦ f,i (298K) ammonia reaction: twice the heat of formation:- 92 kJ/mol ethanol reaction: (- 235 . 1- 52 . 5 + 241 . 8 =- 45 . 8) kJ/mol, HCN reaction: (270 . 2- 227 . 5 = 42 . 7) kJ/mol Problem 2 We run the following reaction 2NH 3 + A O 2 → B H 2 O + C NO 2 with a feed stream of (all percentages are molar ratios) 60% ammonia, 36% oxygen and the rest nitrogen at 400 ◦ C. (a) Determine A , B and C . (b) We now convert all oxygen isothermally. How much heat per mole feed do we need. (Neglect any phase transitions in your calculations.) Solution (a) We have to balance the equation. The left side has 2 nitrogen and 6 hydrogen leading to C = 2 and B = 3 respectively. Now the right side has 7 oxygens leading to A = 3 . 5. (b) The heat of reaction has to be calculated from the heats of formation.(b) The heat of reaction has to be calculated from the heats of formation....
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This note was uploaded on 11/12/2011 for the course ECH 152A taught by Professor Faller during the Fall '09 term at UC Davis.
- Fall '09