Determine ΔG in kJ at a temperature of 261 K given ΔHrxn = 91 kJ and ΔSrxn = 151 J/K.

To determine ΔG (the change in Gibbs free energy) at a given temperature, you can use the equation:

ΔG = ΔH - TΔS

where:
ΔG is the change in Gibbs free energy
ΔH is the change in enthalpy
T is the temperature in Kelvin
ΔS is the change in entropy

In this case, the given values are:
ΔHrxn = 91 kJ
ΔSrxn = 151 J/K
T = 261 K

Now, let's convert the given values to the appropriate units before substituting them into the equation:

ΔHrxn = 91 kJ = 91,000 J (since 1 kJ = 1000 J)
ΔSrxn = 151 J/K (no conversion needed)

Now, substitute the values into the equation:

ΔG = (91,000 J) - (261 K)(151 J/K)

Multiplying the units:

ΔG = 91,000 J - 39,411 J

Finally, perform the subtraction:

ΔG = 51,589 J

To convert J to kJ, divide by 1000:

ΔG = 51.589 kJ

Therefore, ΔG at a temperature of 261 K is 51.589 kJ.