A compound has a percent composition of 81.71% C and 18.29% H. What is the empirical formula of this compound?
1 answer:
Considering the definition of empirical formula, the empirical formula is C₃H₈.
<h3>Definition of empirical formula</h3>The empirical formula is the simplest expression to represent a chemical compound, which indicates the elements that are present and the minimum proportion in whole numbers that exist between its atoms, that is, the subscripts of chemical formulas are reduced to the most integers. small as possible.
<h3>Empirical formula in this case</h3>In this case, in first place you know the percent composition:
- C: 81.71 %
- H: 18.29%
Assuming a 100 grams sample, the percentages match the grams in the sample. So you have 81.71 grams of carbon and 18.29 grams of hydrogen H.
Then it is possible to calculate the number of moles of each atom in the molecule, taking into account the corresponding molar mass:
- C:
= 6.81 moles
- H:
= 18.29 moles
The empirical formula must be expressed using whole number relationships, for this the numbers of moles are divided by the smallest result of those obtained. In this case:
- C:
= 1
- H:
= 2.68 ≅
To express this relationship in the form of simple integers, it is necessary to multiply by a simple number to achieve this:
- C: 1×3 =3
- H:≅
×3= 8
Therefore the C: H mole ratio is 3: 8
Finally, the empirical formula is C₃H₈.
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(1) The quantity of heat required to melt 175 g Cu is 35.88 kJ.
(2) The substance that releases 21.2 kJ of energy when 1.42 mol of it freezes is iron.
<h3>What is heat of fusion?</h3>Heat of fusion is the energy required to melt 1 mole of a substance.
<h3>What is heat of vaporization?</h3>The heat energy required to vaporize 1 mole of a substance has been heat of vaporization.
Heat of fusion of copper (Cu) is given as 13 kJ/mol
Number of moles of 175 g of copper = 175/63.5 = 2.76 moles
Q = nΔH
Q = 2.76 mol x 13 kJ/mol = 35.88 kJ
Thus, the quantity of heat required to melt 175 g Cu is 35.88 kJ.
<h3>Heat of fusion of the substance</h3>ΔH(fus) = Q/n
where;
- n is number of moles
- Q is quantity of heat released
ΔH(fus) = 21.2 kJ / 1.42 mol
ΔH(fus) = 14.93 kJ/mol
From the table the substance with latent heat of fusion of 14.9 kJ/mol is iron.
Thus, the substance that releases 21.2 kJ of energy when 1.42 mol of it freezes is iron.
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