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

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 3.24g of NOBr, 3.09g of NO, and 8.23g of Br2

Part A

Calculate Kc.

Part B

What is the total pressure exerted by the mixture of gases?

Express your answer to three significant figures and include the appropriate units.

Part 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

Part A

mol Br2= 8.23g/160g/mol= 0.0514 mol----->Molarity=0.0514 M/ 5L= 0.01028 M

mol NOBr=3.24g/110g/mol= 0.0295 mol----->Molarity= 0.0295M/5L = 5.9 x 10-3 M

mol NO= 3.09g/30g/mol= 0.103 mol-----> Molarity= 0.103M/ 5L= 0.0206M

Kc=[NO]2[Br2]/[NOBr]2= 0.02062 x 0.01028/(5.9 x 10-3)2= 0.125

Part B

Mol total= 0.0514 +  0.0295 + 0.103= 0.1839 mol

PV=nRT ----> P= nRT/V -----> P= 0.1839mol x 0.082 L.atm/mol.K x 373K/ 5L = 1.13 atm

Part C

2NOBr----->   2NO    + Br2

[NOBr]beggining    0           0      at beggining

[NOBr]beggining -2x 2x     x     at equilibrium

[NOBr]beggining - 2x=  5.9 x 10-3M

x= [Br2]equilibrium -----> x= 0.01028M -------> [NOBr]beggining = 5.9 x 10-3M + 2 x 0.01028M= 0.02646M

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