Naphthalene is a soft covalent solid that is often used in mothballs. Its molar mass is 128.18 g/mol and it contains 93.75% carbon and 6.25% hydrogen. Determine the molecular formula of napthalene from this data.

C10H8

Explanation:

To answer this question, we need to know the atomic masses of carbon and hydrogen. The atomic mass of carbon is 12 amu while that of hydrogen is 1 amu. We start answering the question by dividing the percentages of these elements by their atomic masses.

H = 6.25/1 = 6.25

C = 93.75/12 = 7.8125

We proceed to divide both by the smallest number. This is 6.25

H = 6.25/6.25 = 1

C = 7.8125/6.25 = 1.25

The ratio of both is 1:1.25.

To make a whole number out of these, we multiply through by 4 and that gives 4:5

The empirical formula is thus C5H4

Now, we calculate the molecular formula:

(C5H4)n = 128.18

(5(12) + 4(1))n= 128.18

(60+4)n = 128.18

64n = 128.18

n = 128.18/64

n = approximately 2

The molecular formula is thus C10H8

the enthalpy of formation of water is given as -285.8kj/mol, which states that the enthalpy of formation is negative.

negative enthalpy of formation indicates that the heat is released during the reaction process. the heat is released from reaction to the surroundings the enthalpy is expressed with a negative sign with the energy given out in the reaction process.

the formation of water takes place by giving out heat which is -285.8 kj/mol.