Question

1) The following information is given for n-pentane at 1 atm:

= 36.20°C		(36.20°C) =  J/g
= –129.70°C		(–129.70°C) =  J/g
Specific heat gas = 1.650 J/g °C
Specific heat liquid = 2.280 J/g °C

A 40.00 g sample of liquid n-pentane is initially at –27.30°C. If the sample is heated at constant pressure ( = 1 atm), _______kJ of energy are needed to raise the temperature of the sample to 53.90°C.

2) The following information is given for magnesium at 1 atm:

= 1090.00°C		(1090.00°C) =  J/g
= 649.00°C		(649.00°C) =  J/g
Specific heat solid = 1.017 J/g °C
Specific heat liquid = 1.339 J/g °C

A 48.10 g sample of solid magnesium is initially at 637.00°C. If the sample is heated at constant pressure ( = 1 atm), ________kJ of heat are needed to raise the temperature of the sample to 702.00°C.

3)The following information is given for tin at 1 atm:

= 2270.00°C		(2270.00°C) =  J/g
= 232.00°C		( 232.00°C) =  J/g
Specific heat solid = 0.2260 J/g °C
Specific heat liquid = 0.2430 J/g °C

A 28.40 g sample of solid tin is initially at 207.00°C. If  J of heat are added to the sample at constant pressure ( = 1 atm), which of the following is/are true?

(Select all that apply.)

The sample is a liquid.

The sample is a solid in equilibrium with liquid.

The sample is at a temperature greater than 232.00°C.

The sample is at a temperature of 232.00°C.

The sample is a solid.

Answer 1

Ans 1

Data for n-pentane at 1 atm

boiling point Tb = 36.20 °C

Latent heat of vaporization

Hvap(36.20 °C) = 357.6 J/g

melting point Tm = -129.70 °C

Latent heat of fusion

Hfus(-129.70 °C) = 116.7 J/g

specific heat gas Cpg = 1.650 J/g°C

specific heat liquid Cpl = 2.280 J/g°C

Mass of liquid n-pentane, m = 40 g

Initial temperature T1 = - 27.30°C

n-pentane is in liquid state initially

Heat required to change the temperature from - 27.3 to 36.2c

Q1 = m x Cpl x (T2-T1)

= 40 g x 2.280 J/gK x (36.2 + 27.3)K

= 5791.2 J

Heat required to change the phase from liquid to gas

Q2 = m x Hvap

= 40 g x 357.6 J/g = 14304 J

Heat required to change the temperature from 36.2 to 53.9c

Q3 = m x Cpg x (T2-T1)

= 40 g x 1.650 J/gK x (53.9 - 36.2) K

= 1168.2 J

Total heat required

= 5791.2 + 14304 + 1168.2

= 21263.4 J

= 21.263 kJ