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alexandr402 [8]

3 years ago

5

Compounds like CCl2F2 are known as chlorofluorocarbons, or CFCs. These compounds were once widely used as refrigerants but are n

ow being replaced by compounds that are believed to be less harmful to the environment. The heat of vaporization of CCl2F2 is 289 J/g.
What mass (in grams) of this substance must evaporate to freeze 200g of water initially at 15 degrees C?

(The heat of fusion of water is 334 J/g; the specific heat of water is 4.18 J/g-K.)

2 answers:

steposvetlana [31]3 years ago

8 0

Answer:

274.5 grams of this substance must evaporate to freeze 200 grams of waterof 15 °C

Explanation:

Step 1: data given

The heat of vaporization of CCl2F2 is 289 J/g.

Mass of water (H2O) = 200 grams

Temperature of water = 15.0 °C = 15 - 273 = 288 K

The final temperature of water = the freezing temperature = 0°C = 273 K

The heat of fusion of water is 334 J/g

the specific heat of water is 4.18 J/g*K

Step 2: Calculate the heat release to cool the water from (15.0 °C → 0°C)

Q = m*c*ΔT

⇒with Q = the heat released = TO BE DETERMINED

⇒with m = the mass of water = 200 grams

⇒with c = the specific heat of water is 4.18 J/g*K

⇒with ΔT = the change of temperature of water = 15 °C

Q = 200 * 4.18 * (15)

Q = 12540 J

Step 3: Calculate the energy needed to freeze the water

Q = m*ΔHfus

Q = 200 grams * 334J/g

Q = 66800 J

Step 4: Calculate the total heat released

Q = 12540 + 66800

Q = 79340 J

Step 5: Calculate the mass of this substance must evaporate

Q = m*ΔH(vaporization)

⇒with Q = the total heat released = 79340 J

⇒with m = the mass of CCl2F2 = TO BE DETERMINED

⇒with ΔH(vaporization) = the heat of vaporization of CCl2F2 = 289 J/g.

79340 J = m * 289 J/g

m = 79340 J /289 J/g

m = 274.5 grams

274.5 grams of this substance must evaporate to freeze 200 grams of waterof 15 °C

vova2212 [387]3 years ago

3 0

Answer:

274.5g of CCl₂F₂

Explanation:

To freeze 200g of water yo need to decrease the temperature of water from 15°C to 0°C and then change its phase from solid to liquid. That is:

Decreasing temperature:

q = 4.18J/gK ×200g× (15°C - 0°C)

q = 12540J

In the change of phase:

q = 334 J/g × 200g

q = 66800J

Thus, total heat is:

12540J + 66800J = <em>79340J</em>.

If this heat comes from CCl₂F₂ vaporization, must be evaporated:

79340J × (1g / 289J) = <em>274.5g of CCl₂F₂</em>

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