Thermochemical Equations Practice
1) Using the balanced thermochemical equation below:
2H2 + O2 + 2H20 + 241.8 kJ
How much heat is released when 12.5 grams of hydrogen (Hz) are
completely reacted?

755.625 kj

Explanation:

Given data:

Heat released by two mole of H₂ = 241.8 Kj

Heat released by 12.5 grams of H₂ = ?

Solution:

Number of moles of hydrogen:

Number of moles = mass/ molar mass

Number of moles = 12.5 g/ 2 g/mol

Number of moles = 6.25 mol

Chemical equation:

2H₂ + O₂  →  2H₂O  + 241.8 kj

Now we will determine the heat released by 6.25 moles of hydrogen.

2 mole = 241.8 kj

1 mole =241.8 kj/2 = 120.9 kj

120.9 kj × 6.25 = 755.625 kj

0.00021186 moles of barium nitrate

Explanation:

The given parameter is as follows;

The number of molecules of Barium nitrate Ba(NO₃)₂ = 1.2754 × 10²⁰ molecules

The number of molecule present per mole of Barium nitrate, is given by Avogadro's number, 6.02 × 10²³

1 mole of a substance contains 6.02 × 10²³ molecules

The umber of moles in a substance = (The number of molecules of the substance)/(The number of molecules per mole)

Therefore the number of moles of barium nitrate in 1.2754 × 10²⁰ molecules of barium nitrate = (1.2754 × 10²⁰)/(6.02 × 10²³) ≈ 0.00021186 moles (rounding to 5 significant figures)

The number of moles of barium nitrate present in 1.2754 × 10²⁰ molecules of barium nitrate ≈ 0.00021186 moles