Download HW – Burning Questions

HW – Burning Questions
1. If you take a 5-minute shower, you use about 100,000 mL (25 galloons) of water. The
water needs to be heated from 20ºC to 40ºC.
a. How many calories do you need to warm the water for your shower?
b. How many grams of wood do you need to burn to take a 5-minute shower? The
wood releases 4000 cal/g when you heat it.
c. How many pounds of wood do you need to burn to take a 5-minute shower?
The wood releases 1,814 kcal/lb when you burn it.
2. Which mass of water requires more heat to change its temperature by the amount
specified?
a. 100 g of water from 20ºC to 60ºC.
b. 200 g of water from 20ºC to 45ºC.
3. A piece of wood transfers 3650 calories of heat to 100 mL of water.
a. By how much does the temperature of the water rise?
b. If the initial temperature of the water is 20ºC, what is the final temperature?
c. If the wood weighs 4.2 g, how many calories of heat does a 1 g of wood
transfer?
4. Which cup of water gets hotter?
a. Transfer 450 calories to 100 g of water starting at 25ºC.
b. Transfer 600 calories to 200 g of water starting at 25ºC.
5. Suppose you repeat the Cheeto® experiment, but you place alcohol in the soda can
instead of water. The specific heat capacity of alcohol is 0.58 cal/g ºC.
a. What does it mean that alcohol has a different specific heat capacity? (a
different number of calories are required to heat 1 gram of alcohol by 1 ºC
compared with water)
b. How many calories are required to raise the temperature of 250 g of water by
10ºC? (2500 cal)
c. You will need fewer calories to raise the temperature of 250 g of alcohol by
10ºC. Use the specific heat capacity of alcohol explain why. (for alcohol, you
only need 0.58 cal to raise the temperature of 1 g by 1ºC)
d. How many calories are required to raise the temperature of 250 g of alcohol by
10ºC? (1450 cal)
e. Suppose that you put an ice cube of the same size in the water and in the
alcohol. Which has the capacity to melt more of the ice?