BP and heat capacity

[Meredith92]

Which of the following fluids would be best for a generic radiator of a power plant?
A Distilled water
B Salt water
C Nitrogen Gas
D dehumidified air

Answer: B
I have a few questions about the provided solution:

"Whether the solution is for the radiator of a power plant or any system that absorbs great amounts of heat, the best solution is the one with the greatest heat capacity.."

-- but doesnt a radiator release not absorb heat?

"Choices C and D should not be considered, because they are both gases"

-- why cant we use a gas?

"The addition salt to water increases the heat capacity, allowing salt water to absorb more heat per degree increase and to reach a higher temperature before boiling. "

---I dont really understand how adding salts increases heat capacity.
I do understand that adding salt increases boiling point because of colligative properties/ the nonvolatile solute taking up space on the surface.. but how does this relate to heat capacity?
Thanks!

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[Ibn Alnafis MD]

Which of the following fluids would be best for a generic radiator of a power plant?
A Distilled water
B Salt water
C Nitrogen Gas
D dehumidified air

Answer: B
I have a few questions about the provided solution:

"Whether the solution is for the radiator of a power plant or any system that absorbs great amounts of heat, the best solution is the one with the greatest heat capacity.."

-- but doesnt a radiator release not absorb heat?

"Choices C and D should not be considered, because they are both gases"

-- why cant we use a gas?

"The addition salt to water increases the heat capacity, allowing salt water to absorb more heat per degree increase and to reach a higher temperature before boiling. "

---I dont really understand how adding salts increases heat capacity.
I do understand that adding salt increases boiling point because of colligative properties/ the nonvolatile solute taking up space on the surface.. but how does this relate to heat capacity?
Thanks!

I can only answer one of these questions and will be waiting to see what others think in regards to the other questions.

To understand how radiators work, think about the one in your car. The job of the radiator in cars is to cool down the engine to prevent it from overheating. It does that by circulating a green coolant (water + salts) around the engine to absorb the heat omitted by conduction, because the water is significantly cooler than engine.

 

[mehc012]

Heat energy will only be absorbed as long as there is a temperature difference between the coolant and the heat source. Something with a high specific heat capacity will be able to absorb more (heat) energy before reaching the same temperature. If you think about a gas vs a liquid, gases have: lower IMFs than liquids, and lower density than liquid. Therefore, the gas molecules gain kinetic energy (raise their temperature) more easily than equivalent liquid molecules would, AND have fewer molecules in the same amount of space. It takes less energy to increase the speed of fewer molecules with weaker IMFs, so a gas is really not an ideal coolant. Gases are less efficient coolants than liquids because they will have a much lower specific heat capacity.

Saline, on the other hand, will have a higher total heat capacity than water.
Don't get this confused with having a high specific heat capacity. I really don't know if/how the specific heat capacity of saline compares to pure water. What I do know is that even if they are equal, saline will have a higher total heat capacity because it will remain in liquid form for longer than pure water. If both absorb the same amount of energy/degree raised, but pure water can only increase from 274K to 373K while saline can increase from 270K to 375K (making numbers up, obviously), then saline can absorb more total heat energy, and thus has a higher total heat capacity.

 

[Meredith92]

Thanks that really helps!! Can you also explain why adding salt increases heat capacity?

 

[mehc012]

Thanks that really helps!! Can you also explain why adding salt increases heat capacity?

Agh, my post was incomplete when it first went up...I went back and edited it, but you would probably miss that.

To reiterate, it's important to note the difference between a high specific heat capacity (energy needed to increase T of 1g by 1K) and a high total heat capacity (total capacity to absorb heat energy).

Liquids have a higher specific heat capacity than gases; a solution has a broader liquid range than pure water, and will therefore have a higher total heat capacity than pure water.