2. A scientific law summarizes what has been learned by careful observation of nature.
3. Expressions such as "using up" and "throwing away" are misleading because you would think that matter is lost since you are getting rid of it. However, matter is neither created nor destroyed and atoms are forever.
4.
a. Reactants: Sn-1 H-1 F-1
Products: Sn-1 H-2 F-2
This chemical equation is not balanced because the number of atoms per element on the reactant and products side is not the same, or balanced.
b. Reactants: Si-1 O-2 C-1
Products: Si-1 O-1 C-2
This chemical equation is not balanced because the number of atoms per element on the reactant and products side is not the same, or balanced.
c. Reactants: Al-1 O-3 H-6 Cl-3
Products: Al-1 O-3 H-6 Cl-3
This chemical equation is balanced because the number of atoms per element on the reactant and products side is the same.
5.
a. The coefficient for hydrogen gas is 3.
b. The coefficient for NH3 gas is 2.
c. The coefficient for nitrogen gas is 1.
6.
a. 1 WO3 + 3 H2 --> 1 W + 3 H2O
b. 2 PbS + 3 O2 --> 2 PbO + 2 SO2
c. 4 Fe + 3 O2 --> 2 Fe2O3
7.
a. 1 Ca3(PO4)2 + 3 H2SO4 --> 2 H3PO4 + 3 CaSO4
b. 2 C8H18 + 25 O2 --> 16 CO2 + 18 H2O
8.
a. Yes.
Reactants: Na-2 S-1 O-4 K-2 Cl-1
Product side: Na-2 S-1 O-4 K-2 Cl-1
b. No, when balancing equations, the subscripts remain the same, but the coefficients are altered to balance the equation.
c. 1 Na2SO4 + 2 KCl --> 2 NaCl + 1 K2SO4
9. If you could spend a billion dollars (10 x 10^9 dollars) per second, it would take 400,000 seconds to spend one mole of dollars.
10.
a. O2: 32 g
b. O3: 48 g
c. CaCO3: 100 g
d. Mg(OH)2: 58 g
e. C9H8O4: 180 g
11. Each element's molar mass is according to their atomic weight in 1.00 mol of its substance. Thus, even though copper and sodium have different masses, volumes, and densities, the weight of each atom per mole remains the same.
12.
a. 1 atom.
b. 0.5 atoms.
c. 0.1 atoms.
d. about 0.03 atoms
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