1) Nitrosyl chloride (NOCl) decomposes at high temperature. The equation is

2 NOCl (g) -> 2 NO (g) + Cl2 (g) at 227oC

Using delta Ho = 81.2 kJ and delta So = 128 J/K, calculate the value of the equilibrium constant for this reaction.

I do not know how to start this problem or what formula I should use.

Chemistry(Please help) - DrBob222, Monday, April 23, 2012 at 7:50pm
dGo = dHo - TdSo
Then dGo = -RTlnK

So for delta G= delta H - T delta S it would be delta G= 81200 J/K - 500K(128J/k)

This would equal 17200. Did I do this correctly so far before I move on?

so far so good.

Now I do delta G = -RT lnK

So 17200 = -8.314(500) lnk

17200 = -4157 ln k

This is where I am not sure what to do next do I add 4157 to the left side and then take the ln?

-17200/4157 = ln K

k = about 0.016 (but not exact).

Yes, you have correctly calculated ΔG using the equation ΔG = ΔH - TΔS. ΔH is given as 81.2 kJ, which should be converted to J by multiplying by 1000, and ΔS is given as 128 J/K. The temperature T is given as 227°C, which should be converted to Kelvin by adding 273.15.

So, plugging in the values, we get:

ΔG = (81.2 kJ * 1000 J/kJ) - (227°C + 273.15 K) * 128 J/K
= 81200 J - 500 K * 128 J/K
= 81200 J - 64000 J
= 17200 J

You have correctly calculated ΔG as 17200 J, which is the change in Gibbs free energy for the reaction.

To calculate the equilibrium constant K, you can use the equation:

ΔG = -RTlnK

Since ΔG is known and R is the ideal gas constant (8.314 J/(mol·K)), you can rearrange the equation to solve for K:

K = exp(-ΔG / (RT))

Now, plug in the values:

K = exp(-(17200 J) / ((8.314 J/(mol·K)) * (227°C + 273.15 K)))
= exp(-17200 J / (8.314 J/(mol·K) * 500 K))
= exp(-17200 J / 4157 J/mol)
= exp(-4.135)

Using a calculator or software, you can calculate the value of exp(-4.135) to get the equilibrium constant K.