Question

ethylene glycol is a colorless liquid at room temperature with the following properties

melting point is -12.9°C. boiling point 197.3°C

heat of fusion is 159.50 J/g, heat of vaporization is 1056.87 J/g

heat capacity of the liquid is 2.41 J/g°C, heat capacity of the gas 1.25 J/g°C

a) If you had a sample of ethylene glycol at -10°C, what state would it be in (solid, liquid, or gas)

b) if you decreased the temperature from -10°C to -20°C what phase change would it go through? (melting, freezing, boiling, condensation, sublimation, no change)

c) If you had 5.00g of solid ethylene glycol at -12.9°C, how much energy would be used to take the sample to 10°C? (use 4 sig figs and no unit)

Answer 1

a) At -10 ^oC ethylene glycol is in liquid state because it freezes to solid at -12.9 ^oC.

b) From -10°C to -20°C , Freezing and condensation takes place

Liquid to solid

c)

Mass of ethylene glycol = 5.00 g

At -12.9 C it is a solid undergoes melting at more than this temperature

Heat of fusion = q₁ =

q₁ = 31.9 J

After sample gets liquified we have to calculate the amount heat energy need to rise the temperature of the liquid from -12.9 to 10 C

q₂ = mC(T₂-T₁)

q₂ =5.00(2.41)(22.9)

q₂ = 276.0 J

Total heat required to rise the temperature from -12.9 to 10 c is

Q=q₁+q₂

Q = 276.0 + 31.9 = 307.9 J

Heat energy absorbed = 307.9 J