Oxidation number of an atom is the charge that atom would have if the compound is composed of ions. In neutral substances that contains atoms of one element the oxidation number of an atom is zero. Thus atoms in O2, Ni2, and aluminium all have oxidation number of zero.
In this case, Ni2, the oxidation number of Ni atom is zero,
for NiO4-, assuming oxidation number of Ni is x
(x ×1) + (-2 × 4) = -1
x = + 7
Therefore, the oxidation number goes from 0 to +7
Answer:
2AlCl3 + Ca3N2 - 2AlN+ 3CaCl2
![176.0 \; \text{kJ} \cdot \text{mol}^{-1}](https://tex.z-dn.net/?f=176.0%20%5C%3B%20%5Ctext%7BkJ%7D%20%5Ccdot%20%5Ctext%7Bmol%7D%5E%7B-1%7D)
As long as the equation in question can be expressed as the sum of the three equations with known enthalpy change, its
can be determined with the Hess's Law. The key is to find the appropriate coefficient for each of the given equations.
Let the three equations with
given be denoted as (1), (2), (3), and the last equation (4). Let
,
, and
be letters such that
. This relationship shall hold for all chemicals involved.
There are three unknowns; it would thus take at least three equations to find their values. Species present on both sides of the equation would cancel out. Thus, let coefficients on the reactant side be positive and those on the product side be negative, such that duplicates would cancel out arithmetically. For instance,
shall resemble the number of
left on the product side when the second equation is directly added to the third. Similarly
Thus
and
![-\frac{1}{2} \times (1) + \frac{1}{2} \times (2) - \frac{1}{2} \times (3)= (4)](https://tex.z-dn.net/?f=-%5Cfrac%7B1%7D%7B2%7D%20%5Ctimes%20%281%29%20%2B%20%5Cfrac%7B1%7D%7B2%7D%20%5Ctimes%20%282%29%20-%20%5Cfrac%7B1%7D%7B2%7D%20%5Ctimes%20%283%29%3D%20%284%29)
Verify this conclusion against a fourth species involved-
for instance. Nitrogen isn't present in the net equation. The sum of its coefficient shall, therefore, be zero.
![a + b = -1/2 + 1/2 = 0](https://tex.z-dn.net/?f=a%20%2B%20b%20%3D%20-1%2F2%20%2B%201%2F2%20%3D%200)
Apply the Hess's Law based on the coefficients to find the enthalpy change of the last equation.
![\Delta H _{(4)} = -\frac{1}{2} \; \Delta H _{(1)} + \frac{1}{2} \; \Delta H _{(2)} - \frac{1}{2} \; \Delta H _{(3)}\\\phantom{\Delta H _{(4)}} = -\frac{1}{2} \times (-628.9)+ \frac{1}{2} \times (-92.2) - \frac{1}{2} \times (184.7) \\\phantom{\Delta H _{(4)}} = 176.0 \; \text{kJ} \cdot \text{mol}^{-1}](https://tex.z-dn.net/?f=%5CDelta%20H%20_%7B%284%29%7D%20%3D%20-%5Cfrac%7B1%7D%7B2%7D%20%5C%3B%20%5CDelta%20H%20_%7B%281%29%7D%20%2B%20%5Cfrac%7B1%7D%7B2%7D%20%5C%3B%20%5CDelta%20H%20_%7B%282%29%7D%20-%20%5Cfrac%7B1%7D%7B2%7D%20%5C%3B%20%5CDelta%20H%20_%7B%283%29%7D%5C%5C%5Cphantom%7B%5CDelta%20H%20_%7B%284%29%7D%7D%20%3D%20-%5Cfrac%7B1%7D%7B2%7D%20%5Ctimes%20%28-628.9%29%2B%20%5Cfrac%7B1%7D%7B2%7D%20%5Ctimes%20%28-92.2%29%20-%20%5Cfrac%7B1%7D%7B2%7D%20%5Ctimes%20%28184.7%29%20%5C%5C%5Cphantom%7B%5CDelta%20H%20_%7B%284%29%7D%7D%20%3D%20176.0%20%5C%3B%20%5Ctext%7BkJ%7D%20%5Ccdot%20%5Ctext%7Bmol%7D%5E%7B-1%7D)
Between atoms (one metall and one non metall) form an ionic bond(NaCl)
Answer:
<h2>1.23 moles</h2>
Explanation:
To find the number of moles in a substance given it's number of entities we use the formula
![n = \frac{N}{L} \\](https://tex.z-dn.net/?f=n%20%3D%20%20%5Cfrac%7BN%7D%7BL%7D%20%5C%5C)
where n is the number of moles
N is the number of entities
L is the Avogadro's constant which is
6.02 × 10²³ entities
From the question we have
![n = \frac{6.76 \times {10}^{23} }{6.02 \times {10}^{23} } = \frac{6.76}{6.02} \\ = 1.22923...](https://tex.z-dn.net/?f=n%20%3D%20%20%5Cfrac%7B6.76%20%5Ctimes%20%20%7B10%7D%5E%7B23%7D%20%7D%7B6.02%20%5Ctimes%20%20%7B10%7D%5E%7B23%7D%20%7D%20%20%3D%20%20%5Cfrac%7B6.76%7D%7B6.02%7D%20%20%5C%5C%20%20%3D%201.22923...)
We have the final answer as
<h3>1.23 moles</h3>
Hope this helps you