Figure 3.10. H2O-KCl equilibrium phase diagram. Phases at equilibrium for the system H2O-KCl are shown as a function of chemical composition (weight percent KCl) and temperature. The blue area indicates temperatures and compositions for which a single phase, brine, is present at equilibrium. The crystalline phases are the minerals ice (H2O) and sylvite (KCl). Click on the diagram to see a larger version and to get more information.
For the chemical system H2O-KCl, what phase or phases will coexist at equilibrium for a chemical composition of 10 weight percent KCl at -10°C?
Yes, the point for 10 weight percent KCl and -7°C plots in the 'Ice+Brine" field. No, the point for 10 weight percent KCl and -7°C plots in the 'Ice+Brine" field. To see what phases will be present at equilibrium, plot the composition and temperature on the phase diagram and read the label on the diagram where the values plot.
Yes, the ice-saturated brine at -10°C would have a composition of 13 weight percent NaCl. No, the ice-saturated brine at -10°C would have a composition of 13 weight percent NaCl. You can find this value by using the "Coordinates" button in the enlarged version of Figure 3.10. Look for the composition of the ice-saturation curve at -10°C.
Press "Enter" after you type in the number.
Good thinking. At equilibrium all mixtures of ice and sylvite will begin to melt at -10.8°C. The formation of liquid, in this case brine, is due to a reaction between the ice and the sylvite. Brine is the product of the reaction. Sylvite and brine are consumed in the proportions 19.87 grams of sylvite to 80.13 grams of ice.
No. At equilibrium, all mixtures of ice and sylvite will begin to melt at -10.8°C. The formation of liquid, in this case brine, is due to a reaction between the ice and the sylvite in the proportions 19.87 grams of sylvite to 80.13 grams of ice. Use the phase diagram. To determine the temperature of first melt, find the composition of the rock, then follow that composition up in temperature until it enters a field that contains liquid. In this case, all proportions of ice to sylvite (all compositions) yield the first liquid at -10.8C.
