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atroni [7]
4 years ago
8

The molar heat of fusion of platinum (Pt) is 4.700 kcal/mol. How much heat must be added to 85.5 g of solid platinum at its melt

ing point to completely melt it?
Chemistry
2 answers:
Zolol [24]4 years ago
6 0
The answer is 2.06 kcal
Andre45 [30]4 years ago
4 0
The heat required to completely melt the given substance, platinum, we just have to convert first the given mass in mole and multiply the answer to its molar heat of fusion.. 
                              Hf  = mass x (1/molar mass) x molar heat of fusion
                            Hf = (85.5 g) x (1 mole/195.08 g) x 4.70 kcal/mol
                                   Hf = 2.06 kcal
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Because Ka1 correspond to a dissociation equilibrium. Nitrous acid (HNO₂) losses a proton (H⁺) and gives the monovalent anion NO₂⁻.

b)- The relation between Ka and the free energy change (ΔG) is given by the following equation:

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c)- According to the previous demonstation, at equilibrium ΔG= 0.

d)- In a non-equilibrium condition, we have Q which is calculated with the concentrations of products and reactions in a non equilibrium state:

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Q= ( (5.9 10⁻² M) x (6.7 10⁻⁴ M) ) / (0.21 M)

Q= 1.88 10⁻⁴

We know that   ΔGº= 19092.8 J/mol, so:

ΔG= ΔGº + RT ln Q

ΔG= 19092.8 J/mol + (8.314 J/K.mol x 298 K x ln (1.88 10⁻⁴)

ΔG= -2162.4 J/mol

Notice that ΔG<0, so the process is spontaneous in that direction.

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