Answer:
Number of moles = 0.12 mol
Explanation:
Given data:
Mass of carbonate = 6.5 g
Moles of carbonate = ?
Solution:
Number of moles = mass / molar mass
Molar mass of carbonate = 60 g/mol
Now we will put the values in formula:
Number of moles = 6.5 g/ 60 g/mol
Number of moles = 0.12 mol
Answer:
-7.34 kilo Joules is the change in enthaply when 20.0 grams of nitrogen triiodide decomposes.
Explanation:
Mass of nitrogen triiodide = 20.0 g
Moles of nitrogen triiodide = 

According to reaction, 2 moles of nitrogen triiodide gives 290.0 kilo Joules of heat on decomposition ,then 0.05063 moles of nitrogen triiodide will give :

-7.34 kilo Joules is the change in enthaply when 20.0 grams of nitrogen triiodide decomposes.
The density of He is 1.79 x 10⁻⁴ g/mL
In other words in 1 mL there's 1.79 x 10⁻⁴ g of He.
To fill a volume of 6.3 L the mass of He required
= 1.79 x 10⁻⁴ g/mL * 6300 mL
= 11 277 * 10⁻⁴ g
Therefore mass of He required = 1.1277 g of He
Matter can only me transformed, but not created or destroyed.