Answer:
13.4mol of Mg
Explanation:
Given parameters:
Mass of magnesium = 321g
Unknown:
Number of moles = ?
Solution:
The number of moles of a substance is given as;
Number of moles = 
Molar mass of Mg = 24g/mol
Insert the parameters and solve;
Number of moles = 
= 13.4mol of Mg
Formula for hydroselenic acid: H2Se
This question asks to compare the energy emitted by a piece of iron at T = 603K with the energy emitted by the same piece at T = 298K.
Then you need to use the Stefan–Boltzmann Law
That law states that energy emitted (E) is proportional to fourth power of the to the absolute temperature (T), this is E α T^4 (the sign α is used to express proportionallity.
Then E (603) / E (298) = [603K / 298K]^4 = 16,8
Which meand that the Energy emitted at 603 K is 16,8 times the energy emitted at 298K.
Hydrofluorocarbons (HFCs), perfluorocarbons (PFCs), sulfur hexafluoride (SF6) and nitrogen trifluoride (NF3).
