Changes in state are called phase changes. a phase change is a change from one physical state (gas, liquid, or solid) to another. the amount of energy necessary to melt 1 mole of any solid is called its enthalpy of fusion. the amount of energy necessary to vaporize 1 g of any substance is called its enthalpy of vaporization. the enthalpy of fusion of solid sodium is 2.60 kj/mol. calculate the energy required to melt 43.6 g of solid sodium.

the energy required is Q = 4.9 kJ

Explanation:

Since the energy required is

Q = L * n

where L = molar enthalpy of fusion of solid sodium =  2.60 kJ/mol

and n = number of moles involved

also we know that

n= m/ M , where m= mass involved , M = molecular weight of sodium

the molecular weight of sodium is M= 23 g / mol

therefore

Q = L * n = L* m / M

replacing values

Q = L* m / M =  2.60 kJ/mol * 43.6 g/ (23 g / mol) = 4.9 kJ

Q = 4.9 kJ

thus the energy required is Q = 4.9 kJ

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