Which describes the elements in a given group of the periodic table?

Consider the following reaction: A2 + B2 → 2AB ΔH = –321 kJ Bond energy (A2) = 1/2AB Bond energy (B2) =393 kJ/mol. What is the n

nirvana33 [79]

Answer: The numerical value for Bond energy of $A_2$ is -238 kJ/mol

Explanation:

The balanced chemical reaction is,

$A_2+B_2(g)\rightarrow 2AB$ $\Delta H=-321kJ$

The expression for enthalpy change is,

$\Delta H=\sum [n\times B.E(reactant)]-\sum [n\times B.E(product)]$

$\Delta H=[(n_{A_2}\times B.E_{A_2})+(n_{B_2}\times B.E_{B_2}) ]-[(n_{AB}\times B.E_{AB})]$

$\Delta H=[(1\times x)+(1\times B.E_{B_2}) ]-[(2\times 2x)]$

where,

n = number of moles

If $B.E_{A_2}=x$ $B.E_{AB}=2x$

Now put all the given values in this expression, we get

$-321=[(1\times x)+(1\times 393)]-[(2\times 2x)]$

$x=-238kJ/mol$

Therefore, the bond energy of $A_2$ is -238 kJ/mol

6 0

3 years ago

FeSO4 • 7H2O

Mrac [35]

Answer:

1. Percent by mass of H₂O = 45.3%

2. Percent by mass of anhydrous Salt (FeSO₄) = 54.7 %

Explanation:

Data Given

Formula of the Molecule = FeSO₄ • 7H₂O

% by mass water (H₂O) = ?

% by mass FeSO₄ = ?

________________________________________

> First of all find the atomic masses of each component in a molecule

For H₂O atomic masses are given below

H = 1 g/mol

O = 16 g/mol

> Then find the total mass of H₂O in haydrated salt

7H₂O = 7 (2x1 +1x16) g/mol

7H₂O = 7 (2+16) g/mol

7H₂O = 7 (18) g/mol

7H₂O = 126 g/mol

> find total Molar Mass of Molecule:

Molar Mass of FeSO₄ • 7H₂O = [56+ 32 + 16x4] + 7(2+16)

Molar Mass of FeSO₄ • 7H₂O = [56+ 32 + 64] + 126

Molar Mass of FeSO₄ • 7H₂O = 278

Now to find the mass by percent of H₂O

Formula used to find the mass by percent of a component

Percent composition of H₂O = mass of H₂O in Molecule / molar mass of FeSO₄ • 7H₂O x 100%

Put the values

Percent by mass of H₂O = 126 (g/mol) / 278 (g/mol) x 100%

Percent by mass of H₂O = 0.4532 x 100%

Percent by mass of H₂O = 45.3%

_______________________________________________

> First of all find the atomic masses of each component in a molecule

For anhydrus salt (FeSO₄) atomic masses are given below

Fe = 56 g/mol

S= 32 g/mol

O = 16 g/mol

> Then find the total mass of FeSO₄ in haydrated salt

FeSO₄ = (56x1 + 32 + 4x16) g/mol

FeSO₄ = ( 56 + 32 + 64) g/mol

FeSO₄ = 152 g/mol

> find total Molar Mass of Molecule:

Molar Mass of FeSO₄ • 7H₂O = [56+ 32 + 16x4] + 7(2+16)

Molar Mass of FeSO₄ • 7H₂O = [56+ 32 + 64] + 126

Molar Mass of FeSO₄ • 7H₂O = 278

Now to find the mass by percent of FeSO₄

Formula used to find the mass by percent of a component

Percent composition of FeSO₄ = mass of FeSO₄ in Molecule / molar mass of FeSO₄ • 7H₂O x 100%

Put the values

Percent by mass of FeSO₄ = 152 (g/mol) / 278 (g/mol) x 100%

Percent by mass of FeSO₄ = 0.547 x 100%

Percent by mass of FeSO₄ = 54.7 %

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