Answer:
1 valence - Alkali Metals: Li Lithium, Na Sodium, K Potassium
2 valence - Alkaline Earth Metals: Be Beryllium, Mg Magnesium, Ca Calcium
3 valence - Non-metals: B Boron, Al Aluminium
4 valence - Non-metals: C Carbon, Si Silicon
5 valence - Non-metals: N Nitrogen, P Phosphorus
6 valence - Non-metals: O Oxygen, S Sulfur, Se Selenium
7 valence - Halogens: F Fluorine, Cl Chlorine, Br Bromine
8 valence - Noble Gases: He Helium, Ne Neon, Ar Argon
From the chemical formula the total mass of the compound can be determined. The mass of the 1 mole of the compound is its molar mass. The atom by which the molecule is generated, the mass of these atoms are expressed in terms of amu or atomic unit mass, but after formation of a molecule in a particular ratio the mass of each of the atom becomes the total molecular weight of the generated molecule. In this case the molecule posses three atoms X, Y and Z which are in a ratio of 2:2:7. Thus the chemical formula of the compound can be written as
.
So the total mass of the compound in amu is {(2×47)+(2×42)+(7×16)} = {94+84+112}=290 amu.
Thus 1 mole of the compound contains 290 amu or 290 g by mass.
Henceforth 20 gram of the compound is equivalent to (20/290) = 0.068 mole.
Answer:
16.9g of H₂O can be formed
Explanation:
Based on the chemical reaction, 2 moles of H₂ react per mole of O₂. To anser this question we must find limiting reactant converting the mass and volume of each reactant to moles:
<em>Moles H₂ -Molar mass: 2.016g/mol-:</em>
8.76g * (1mol / 2.016g) = 4.345 moles
<em>Moles O₂:</em>
PV = nRT
PV/RT = n
P = 1atm at STP
V = 10.5L
R = 0.082atmL/molK
T = 273.15K at STP
n = 1atm*10.5L / 0.082atmL/molK*273.15K
n = 0.469 moles of oxygen
For a complete reaction of 4.345 moles moles of hydrogen are required:
4.345 moles H2 * (1mol O2 / 2mol H2) = 2.173 moles of O2 are required. As there are just 0.469 moles, Oxygen is limiting reactant
Now, 1 mole of O2 produce 2 moles of H2O. 0.469 moles will produce:
0.469 moles O₂ * (2 moles H₂O / 1mol O₂) = 0.938 moles H₂O.
The mass is -Molar mas H₂O = 18.01g/mol-:
0.938 moles * (18.01g/mol) =
<h3>16.9g of H₂O can be formed</h3>
The change in internal energy (ΔΕ) of a system : -8 kJ
<h3>Further explanation </h3>
The laws of thermodynamics 1 state that: energy can be changed but cannot be destroyed or created
The equation is:

Energy owned by the system is expressed as internal energy (U)
This internal energy can change if it absorbs heat Q (U> 0), or releases heat (U <0). Or the internal energy can change if the system does work or accepts work (W)
The sign rules for heat and work are set as follows:
• The system receives heat, Q +
• The system releases heat, Q -
• The system does work, W -
• the system accepts work, W +
5 kJ of work is done on the system : W = +5 kJ
releases 13 kJ of energy to the surroundings : Q = -13 kJ
