Question

How much heat is required to convert 32.5 g of ethanol at 28 ∘C to the vapor phase at 78 ∘C?

Express your answer using two significant figures.

Answer 1

Temperature change of ethanol 28⁰C to 78⁰C

T = 78 - 28 = 50⁰C

specific of ethanol = 2.46 J/ g ⁰C

mass of ethanol = 32.5 gm

q₁ = mass of ethanol     specific heat of ethanol    T

= 32.5 2.46 50

q₁ = 3997.5 J = 3.9975 KJ

Phase change from liquid ethanol to vapour ethanol

Heat of vaporization of ethanol = 39.3 KJ/mol

That mean to convert 1 mole of liquid ethanol to 1 mole of vapour ethano without change in temperature require heat 39.3 KJ/mol

1 mole of ethanol = 46.06844 gm

to convert 46.06844 gm of liquid ethanol to vapour ethanol without change in temperature require heat 39.3 KJ then to convert 32.5 gm of liquid ethanol to vapour ethanol without change in temperature require heat

32.5 39.3 / 46.06844 = 27.725 KJ

q₂ = 27.725 KJ

to convert 32.5 g of ethanol at 28 ∘C to the vapor phase at 78 ∘C required heat = 3.9975 + 27.725 = 31.7225 KJ