1) While Laurie is boiling water to cook spaghetti, the phone rings, and all 1.5 kg of water boils away during her conversation.If the water was initially at 15℃, how much heat must have been gained for all of it to turn into a water vapor?
2)By January, the 3.0 kg of water in the birdbath in the Robyn's backyard has frozen to a temperature of 7.0℃. As the season changes, how much heat must be added to the water to make it a comfortable 25℃ for the birds?
heat=mass*lf+ mass*cice*(7)+mass*cwater*25
This assumes an initial temp of the ice at MINUS 7C
To answer these questions, we can use the formula for heat transfer:
Q = m * c * ΔT
where:
Q is the heat transferred (in Joules)
m is the mass of the substance (in kilograms)
c is the specific heat capacity of the substance (in J/(kg·℃))
ΔT is the change in temperature (in ℃)
1) To find the heat gained to boil away all the water, we need to calculate the change in temperature first:
ΔT = boiling point - initial temperature
The boiling point of water is 100℃, so the change in temperature is:
ΔT = 100℃ - 15℃ = 85℃
Next, we need to substitute the values into the formula:
Q = 1.5 kg * (mass of water) * 85℃
The specific heat capacity of water is approximately 4,186 J/(kg·℃). Substituting this value in, we can calculate the heat gained:
Q = 1.5 kg * 4,186 J/(kg·℃) * 85℃
2) To find the heat needed to raise the temperature from 7.0℃ to 25℃, we can follow a similar process:
ΔT = final temperature - initial temperature
ΔT = 25℃ - 7.0℃ = 18℃
Substituting the values into the formula:
Q = 3.0 kg * (mass of water) * 18℃
Again, we use the specific heat capacity of water (4,186 J/(kg·℃)) to find the heat needed:
Q = 3.0 kg * 4,186 J/(kg·℃) * 18℃
By calculating these expressions, you will get the values of Q, which represent the amount of heat that needs to be transferred to achieve the desired changes in these scenarios.