Question

1. Calculate the amount of heat required to convert 1 g of liquid water at 67°C to steam at 100°C. The specific heat of liquid water is 4.18 J/g°C and the heat of vaporization is 40.7 kJ/mol.

2400 J

2.2 kJ

8.31 J

22.6 kJ

40.8 kJ

2. Which one of the following is true about surfactants?

they act to decrease surface tension

they form micelles on the surface of water

none of these

they are generally very small, highly charged molecules

3. Consider a liquid sealed in a rigid vessel. As the vessel is heated more and more vapor fills the space above the liquid, the liquid level drops, and the interface between the liquid and gas gets increasingly faint. Eventually, the line between liquid and gas disappears. What substance is in the container at that point?

supercritical fluid

single atoms

plasma

gas

solid

Answer 1

1)

Ti = 67.0

Tf = 100.0

here

Cl = 4.18 J/g.oC

Heat required to convert liquid from 67.0 oC to 100.0 oC

Q1 = m*Cl*(Tf-Ti)

= 1 g * 4.18 J/g.oC *(100-67) oC

= 137.94 J

Lv = 40.7KJ/mol =

40700J/mol

Lets convert mass to mol

Molar mass of H2O = 18.016 g/mol

number of mol

n= mass/molar mass

= 1.0/18.016

= 0.0555 mol

Heat required to convert liquid to gas at 100.0 oC

Q2 = n*Lv

= 0.0555 mol *40700 J/mol

= 2259 J

Total heat required = Q1 + Q2

= 137.94 J + 2259 J

= 2397 J

Answer: 2400 J

I am allowed to answer only 1 question at a time