Unit 3: #15-19

Question 1

15. Sketch the energy bar chart for water vapor at 150°C that condenses to liquid water at room temperature. Graph the energy bar chart.

Answer 1

Eth has 4 bars. Eph has 4 bars. 4 bars leave the water. Eth has 2 bars. Eph has 2 bars.

/solid Eth, —solid and liquid Eph, /liquid Eth, —liquid and gas Eph

Question 2

18. How much energy must be transferred to 45g of liquid water that starts at 10°C in order to boil it completely?

Answer 2

/Q1, —Q2.

Q1=MCΔT = (45g)(4.10J/g°C)(90°C) =16,929J
Q2=mHv = (45g)(2260J/g) =101,700J
Total = 120,000J

Question 3

19a. In a classroom demonstration, Miss frizzle heats a 79.16gram sample of zinc in a Bunsen burner flame. The specific heat capacity of zinc is 0.390J/g°C. She then submerges the zinc in a coffee cup calorimeter containing 100.0g of water. The water increases its temperature from 24.5°C to 29.5°C. What is the quality of heat gained by the water? Lost by the zinc?

Answer 3

-qzinc = +qwater
=MCΔT = (100.0g)(4.18J/g°C)(5.0°C)
= 2090J of water, -2090J of zinc

Question 4

19b. In a classroom demonstration, Miss frizzle heats a 79.16gram sample of zinc in a Bunsen burner flame. The specific heat capacity of zinc is 0.390J/g°C. She then submerges the zinc in a coffee cup calorimeter containing 100.0g of water. The water increases its temperature from 24.5°C to 29.5°C. What was the initial temperature of the zinc before being plunged into the water?

Answer 4

-2090J = MCΔT = (79.16g)(0.390J/°C)ΔT
ΔT = -67.7°C
ΔT = Tf - Ti
-67.7 = 29.5 - Ti
Ti = 97.2°C