how many calories are needed to convert 20.0g of water at 25 Celsius to steam at 100 Celsius?
To determine the number of calories needed to convert a given amount of water from a lower temperature to steam at a higher temperature, we need to understand the process of heating and phase change.
In this case, we need to calculate the heat energy required to raise the temperature of the water from 25°C to 100°C (as we assume no pressure change) and then the heat energy needed for the phase change from liquid water to steam at 100°C.
The specific heat capacity of water is defined as 1 calorie/gram·°C. This means that it takes 1 calorie of heat energy to raise the temperature of 1 gram of water by 1 degree Celsius.
First, we calculate the amount of heat energy required to raise the temperature of the water:
Heat energy = mass × specific heat capacity × temperature change
Given:
mass of water = 20.0 grams
specific heat capacity of water = 1 calorie/gram·°C
temperature change = (100°C - 25°C) = 75°C
Heat energy for temperature change = 20.0 grams × 1 calorie/gram·°C × 75°C
= 1,500 calories
Next, we calculate the heat energy required for the phase change from liquid water to steam. For this phase change, we use the heat of vaporization for water. The heat of vaporization for water is approximately 540 calories/gram.
Heat energy for phase change = mass × heat of vaporization
Given:
mass of water = 20.0 grams
heat of vaporization of water = 540 calories/gram
Heat energy for phase change = 20.0 grams × 540 calories/gram
= 10,800 calories
Finally, we add the heat energy for temperature change and phase change together:
Total heat energy = Heat energy for temperature change + Heat energy for phase change
= 1,500 calories + 10,800 calories
= 12,300 calories
Therefore, it would require approximately 12,300 calories to convert 20.0 grams of water at 25°C to steam at 100°C.
q1 = heat needed to convert water at 25 to water at 100
q1 = mass x specific heat H2O x (Tfinal-Tinitial)
(Note:) Tf is 100; Ti is 25
q2 = heat needed to convert H2O to steam.
q2 = mass H2O x heat vaporization.
qtotal = q1 + q2