Consider the gold-platinum system which has a value of delta w of -4250 J/mole;

(a) Calculate the enthalpy of mixing for a solution of 10% platinum and 90% gold. Express your answer in units of kJ/mole.

(b) Is the dissolution of 10% platinum into gold an endothermic or an exothermic process?

Exothermic as the change in enthalpy is negative.
Endothermic as the change in enthalpy is positive.
Impossible to tell without considering the entropy of the system.

To calculate the enthalpy of mixing for the gold-platinum system, we need to use the given value of delta w (-4250 J/mol). The enthalpy of mixing is given by the equation:

ΔH_mix = X_A * X_B * delta w

where X_A and X_B are the mole fractions of gold and platinum, respectively.

(a) In this case, we have a solution with 10% platinum and 90% gold. To calculate the mole fractions, we first need to convert the percentages to decimal fractions:

X_A = 0.90
X_B = 0.10

Now we can substitute the values into the equation to calculate the enthalpy of mixing:

ΔH_mix = 0.90 * 0.10 * (-4250 J/mol)
= -382.5 J/mol.

To express the answer in kJ/mol, we divide by 1000:

ΔH_mix = -382.5 J/mol / 1000
≈ -0.383 kJ/mol.

Therefore, the enthalpy of mixing for the solution is approximately -0.383 kJ/mol.

(b) The sign of the enthalpy change determines if the process is endothermic or exothermic. Since the enthalpy of mixing is negative (-0.383 kJ/mol), it indicates that the dissolution of platinum into gold is an exothermic process.