For a certain Chemical reaction, you find that delta H = -100kJ and delta S = -200 J/K. What is the Gibbs free energy for the reaction at:
(a) room temperature
(b) 800 C
(c) comment on whether the reactions are spontaneous or not
The Gibbs free energy (ΔG) can be calculated using the equation:
ΔG = ΔH - TΔS
where ΔH is the change in enthalpy, ΔS is the change in entropy, and T is the temperature in Kelvin.
Let's calculate the Gibbs free energy for the reaction at different temperatures:
(a) Room temperature is usually around 298 K. So, substituting the given values into the equation:
ΔG = -100 kJ - (298 K)(-200 J/K)
ΔG = -100 kJ + 59.6 kJ
ΔG = -40.4 kJ
(b) To calculate ΔG at 800 °C, we need to convert it into Kelvin:
800 °C = 1073 K
ΔG = -100 kJ - (1073 K)(-200 J/K)
ΔG = -100 kJ + 214.6 kJ
ΔG = 114.6 kJ
(c) To determine whether the reactions are spontaneous or not, we can analyze the sign of ΔG.
If ΔG < 0, the reaction is spontaneous and tends to proceed in the forward direction.
If ΔG > 0, the reaction is non-spontaneous and tends to proceed in the reverse direction.
If ΔG = 0, the reaction is at equilibrium.
(a) ΔG = -40.4 kJ, since ΔG < 0, the reaction is spontaneous.
(b) ΔG = 114.6 kJ, since ΔG > 0, the reaction is non-spontaneous.
Therefore, at room temperature the reaction is spontaneous, but at 800 °C it becomes non-spontaneous.