metal sodium 2.60 kJ/mol 97.0 kJ/mol 1.00 g

metal sodium 2.60 kJ/mol 97.0 kJ/mol 1.00 g

 

 

The molar heat of fusion of sodium metal is 2.60 kJ/mol, whereas its heat of vaporization is 97.0 kJ/mol.

a. Why is the heat of vaporization so much larger than the heat of fusion?

b. What quantity of heat would be needed to melt 1.00 g sodium at its normal melting point?

c. What quantity of heat would be needed to vaporize 1.00 g sodium at its normal boiling point?

d. What quantity of heat would be evolved if 1.00 g sodium vapor condensed at its normal boiling point?

 

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a. Why is the heat of vaporization so much larger than the heat of fusion?

 

분자든, 원자든 원리는 동일하다.

고체, 액체, 기체 상태에서, 원자간 거리를 생각해보면,

고체 < 액체 <<< 기체

 

 

원자끼리 붙어있는 것을 분리시켜 떼어놓으려면 에너지가 필요한데,

더 멀리 확실하게 떼어놓으려면 더 많은 에너지가 필요할 것이다.

이 때문에, heat of vaporization >>> heat of fusion

 

 

비유하면,

> heat of fusion = 비행기가 이륙하는데 필요한 에너지

> heat of vaporization = 우주선이 지구 중력을 벗어나는데 필요한 에너지

 

 

 

 

b. What quantity of heat would be needed to melt 1.00 g sodium at its normal melting point?

 

Na의 몰질량 = 22.99 g/mol

 

 

(1.00 g) (1 mol / 22.99 g) (2.60 kJ/mol)

= (1.00) (1 / 22.99) (2.60)

= 0.113 kJ

 

 

 

 

c. What quantity of heat would be needed to vaporize 1.00 g sodium at its normal boiling point?

 

(1.00 g) (1 mol / 22.99 g) (97.0 kJ/mol)

= (1.00) (1 / 22.99) (97.0)

= 4.22 kJ

 

 

 

 

d. What quantity of heat would be evolved if 1.00 g sodium vapor condensed at its normal boiling point?

 

(1.00 g) (1 mol / 22.99 g) (-97.0 kJ/mol)

= (1.00) (1 / 22.99) (-97.0)

= -4.22 kJ