At standard atmospheric pressure, the solid form of carbon dioxide called \"dry

Question

At standard atmospheric pressure, the solid form of carbon dioxide called "dry ice" undergoes a phase change not to a liquid, but straight to a gas. This process is called sublimation, and like other phase transitions, heat energy is required. In this case, it is the latent heat of sublimation, which for carbon dioxide is 573 kJ/kg at the sublimation temperature of 78.5°C. If 158 g of dry ice is dropped into 0.50 L of water at room temperature (20°C), how much of the water will turn to ice by the time all the dry ice has sublimated? Note: When dry ice becomes a gas, the gas bubbles out of the system.

Explanation / Answer

When the dry ice sublimes (turns into a gas), it takes away energy from water (then the water, having lost that

energy will freeze. So the dry ice takes away 573 kJ/kg*0.158 kg= 90.534 kJ = 90534 J

Now you have the 0.5 L of water which lost all that energy in the form of heat. First ALL of the water will go from 20

degrees to 0 degrees, so subtract that from above. E=mcT where c=4.1868 J/(g*C)

90534 J - 0.5L (1000 g/1 L of water)*4.1868* (20-0) = 48666 J

So now we can calculate how much water was able to turn into ice. (Remember, when water is freezing, the

temperature stays at 0, and the temperature only changes after all of the water has frozen. ) So we can equate this

to find the mass of water turning to ice by whatever energy hasnt been accounted for.

48666 = mass*333

Mass=48666 J /333 = 146.14 g = 0.14614 kg

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