Posted: April 24th, 2017

How many btu are needed to change 10 pounds of ice at 5 degree Fahrenheit to steam at 250 degree Fahrenheit?

Problem 1.

How many btu are needed to change 10 pounds of ice at 5 degree Fahrenheit to steam at 250 degree Fahrenheit?

Solution:

The first step: we convert the temperatures given in Fahrenheit into the temperatures in Celsius:

5 degree Fahrenheit = -15 C

250 degree Fahrenheit = 121 C

Then we can see that initially we have m=10 pounds = 4.5 kg of ice and finally we have m = 4.5 kg of vapor. Therefore the whole process can be considered as the combination of the following processes:

(1) heating the ice from -15 C to 0 C;

(2) melting of ice at fixed temperature 0 C. After this process the ice becomes water.

(3) heating the water from 0 C to 100 C.

(4) vaporization of water at fixed temperature100 C. After this process the water becomes vapor.

(5) heating the vapor from 100 C to 121 C.

problem 2

An ice cube having a mass of 50 grams and an initial temperature of -10 degrees Celsius is placed in 400 grams of 40 degrees Celsius water. What is the final temperature of the mixture if the effects of the container can be neglected?

Problem 3.

One day the relative humidity is 90% and the temperature is 25 degrees Celsius. How many grams of water will condense out of each cubic meter of air if the temperature drops to 15 degrees Celsius? How many energy does the condensation from each cubic meter release?