A sample of nitrosyl bromide (NOBr) decomposes according to the equation 2NOBr(g

Question

A sample of nitrosyl bromide (NOBr) decomposes according to the equation 2NOBr(g)2NO(g)+Br2(g) An equilibrium mixture in a 5.00-L vessel at 100 C contains 3.25 g of NOBr, 3.02 g of NO, and 8.04 g of Br2. A:Calculate Kc. B:What is the total pressure exerted by the mixture of gases? Express your answer to three significant figures and include the appropriate units. C:What was the mass of the original sample of NOBr? Express your answer to four significant figures and include the appropriate units.

Explanation / Answer

The equation of the above reaction is

2NOBr(g)2NO(g)+Br2(g)

Divide the mass of each component in the mixture by its molecular mass in g/mole. This gives the corresponding numbers of moles. Then divide these by 5.00 L; the result gives the concentrations in molarity. Kc is then calculated by:
Kc = [NO]²[Br2] / [NOBr]².

=> Kc =  [ 3.02]²[8.04] / [3.25]².

=> Kc = 6.942
2.) Add all the number of moles calculated in 1.). Then substitute into:
P = nRT/V;
since we are given T and V.

moles of NOBr = 3.25 / 109.92 = 0.0295 mol

moles of NO = 3.02 / 30 = 0.1006 mol

Mol mass of Br2 = 8.04 / 159.8 = 0.0503 mol

Total no. of moles = 0.0295 + 0.1006 + 0.0503 = 0.1804 = n

T = 283 K

V = 5 L

so P = nRT/V;

=> P =  0.1804 * 8.314 * 283 / 5 = 84.891 bar

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