How much energy (in J) is required to raise the temperature of 500 g of water fr

Question

How much energy (in J) is required to raise the temperature of 500 g of water from 20 to 100C, and then turn it to steam at 100C?

Temperature is a "sensed" property of matter. Several different temperature scales
have been devised over the centuries, all of them arbitrary because the values of certain
fixed points are arbitrary. The most common Metric scale is named after the physicist
Celsius; in times gone by (e.g., when your prof was a boy) it was called the Centigrade
scale. In Celsius, the zero point is fixed by the melting point of ice, and the 100 point by
the boiling point of water. The most common English system is named after Dr. Fahrenheit,
who fixed the zero point at the lowest value he could create with a mixture of ice and salt,
and the 100 point at human body temperature. Here are some points in both scales:
Phenomenon oC oF
Dry ice evaporates -78.5 -109.3
Water ice melts 0 32
Warm spring day 75 24
Body temperature 37 98.6
Water boils 100 212
Absolute zero -273 -460 (to nearest degree)
(all molecular motion stops)
Most physics problems require the temperature to be stated in absolute units, called
degrees Kelvin, or simply Kelvins. The zero point for Kelvins is absolute zero. To obtain
Kelvins (K) from Celsius, add 273 to the Celsius temperature.
Rather than give you conversion equations, I'll simply note that unit conversion apps are
available all over the Web. I like the one at http://www.onlineconversion.com.

Explanation / Answer

This one basically combines the two steps. You first have to increase the temperature of the water to 373K (which is also 100 degrees Celsius, the boiling pt. of water), then use the heat of vaporization of water, which is 539.423 cal/g*K. First step: increase temp. of water to 373K. Use q=mC?T. (500g) * (1cal/g*K) * (80K) = 40,000cal ADD this to the energy needed to turn this 100 degree C water to steam: (500g) * (539.423 cal/g*K) = 269,711.5cal 269,711.5cal + 40,000cal = 309,711.5 cal, or 309.711kcal.

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