Question

Ccl2f2 is considered to be environmentally safe and is used as a refrigerant. The heat of vaporization of ccl2f2 is 289 j/g. What mass of this substance must evaporate in order to freeze 2 moles of water initially at 20°c? The heat of fusion of water is 334 j/g and the specific heat of water is 4.18 j/g-k.

Answer 1

Answer:

52.1 gram of CCl2F2 must evaporate

Explanation:

Step 1: Data given

The heat of vaporization of CCl2F2 is 289 j/g

Number of moles water = 2.0 moles

Initial temperature of water = 20.0 °C

The heat of fusion of water is 334 j/g

The specific heat of water is 4.18 j/g *k

Step 2: Calculate mass H2O

Mass = 2.0 moles * 18.02 g/mol

Mass H2O = 36.04 grams H2O

Step 3: Cooling of liquid H2O from 20.0 °C to 0°C

Q = m*c* ΔT

⇒Q = heat lost when cooling = TO BE DETERMINED

⇒ m = the mass of water = 36.04 grams

⇒c = the specific heat of water = 4.18 J/g*K = 4.18 J/g°C

⇒ΔT = the change in temperature =  20.0 °C

Q = 36.04 * 4.18 *20.0

Q = 3012.9 J

Step 4: Converting liquid H2O to solid H2O (ice) = freezing

Q = m*Hfus

⇒with Q = the heat lost when cooling = TO BE DETERMINED

⇒with m = the mass of water = 36.04 grams

⇒with Hfus = The heat of fusion of water = 334 j/g

Q = 36.04 * 334

Q = 12037 .4 J

Step 5: The total heat lost

Q = 3012.9 + 12037.4

Q = 15050.3 J

Step 6: Calculate mass CCl2F2 needed

Mass CCl2F2 = Q / hvap

Mass CCl2F2 = 15050.3 J / 289 J/g

Mass CCl2F2 = 52.1 grams

52.1 gram of CCl2F2 must evaporate

Answer 2

Answer:

52.08grams

Explanation:

Heat of fusion is the energy needed to transform solid water into liquid water. Hess's Law.

The temperature change Liquid water to Solid Ice. 20 degrees C --> 0 degrees C. is 20 degree C.

The heat needed for this  is =  4.184 J/(g*C) * (36 grams of water) * 20 degrees C =  3012 joules of energy.

Liquid water to solid water.

Heat of fusion of water is 335j/g = 6.02kJ/mol

The heat needed for this is 6.02 kJ/mol * 2 moles of water = 12.04 kJ = 12040 joules of energy.

Adding the  two energies, we have a total energy iof 15052 joules.

15052 joules = H(vap of CCl2F2) * grams of CCl2F2 needed = 289 J/g * x grams 15052 / 289 = 52.08 grams needed.