KEY H4_SP 2011

KEY H4_SP 2011 - Chem 112 Homework4 SP2011 1 Guide(3...

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Chem 112 Homework 4 SP 2011 Answer Key and Solutions Guide 1. (1) Condition (2) yes or no (3) Justify your “yes” or “no” in column 2 k forward = k backward no the “k’s” are the rate constants for the forward and reverse reactions, respectively. There is no requirement that they ever be equal, although coincidentally, it could happen. The k’s are functions of the geometric factor and the Ε activation for each reaction and are extremely unlikely to be equal. [A] = [B] no there is no requirement that the equilibrium concentrations of the product and reactant be the same. In fact, it is a highly improbably condition and occurs only if K eq = 1 for this simple, two-participant reaction. rate forward = rate backward yes when the rate of the forward and reverse reactions are equal, there will be no net change in concentration of any participant in the reaction, which is the definition of equilbrium P A = P B no the partial pressures of gases are directly proportional to their concentrations, see answer for the 2 nd line above. It applies here. no reaction is occurring no no NET reaction is occurring but both the forward and reverse reactions may be occurring to a great extent. It is a very busy world at the molecular/atomic level! 2. Graders: Student MUST show that there is at least some of each reactant left, in order to establish the equilibrium. Using the stoichiometry of the reaction, determine if there is enough of the two reactants to have produced the indicated amount of product and still have some left . If either reactant is all used up, then this equation does not apply to the system and this equilibrium cannot be occurring. Volume was not stated, so I assume V = 1.00 L, then molarities are numerically equal to the number of moles. (i) Start by finding change in amount of PH 3 (g) 1.27 x 10 −4 mol 6.05 x 10 −5 mol = 6.65 x 10 −5 mol (ii) Find amount of P 4 required to produce this much product: 6.65 x 10 −5 mol PH 3 (g) produced x 3 4 4 1 PH mol P mol = 1.66 x 10 −5 mol P 4 required. Mass P 4 required = 1.66 x 10 −5 mol P 4 x atom g x mol atoms 9738 . 30 4 = 0.00206 g P 4 req’d There are 0.500 g available, so this reactant is not used up. (iii) Find amount of H 2 required to produce this much product: 6.65 x 10 −5 mol PH 3 (g) produced x 3 2 4 6 PH mol H mol = 9.975 x 10 −5 mol H 2 required. There are 3.86 x 10
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KEY H4_SP 2011 - Chem 112 Homework4 SP2011 1 Guide(3...

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