Question

A)
When the products of a reaction are known, which fact can always be deduced about the reactants?
(1 point)
the mass of each reactant.
the state of the reactants.
the number of atoms in the reactants.
the number of reactants.
A)
Hydrogen peroxide decomposes into water & oxygen according to the following reaction.
Based on the law of conservation of mass, which could be the product of the reaction?
(1 point)
2H2O2 → Water + Oxygen
2
O
+
H
2
O
2
4
O
+
2
H
2
O
2
O
+
H
2
O
2
2
O
+
2
H
2
O
2

A)
Calcium carbonate (
) can undergo a chemical reaction to produce calcium oxide (
) andcarbon dioxide (
). Which possible masses of calcium oxide and carbon dioxide can form when200g of calcium carbonate undergoes this chemical reaction?
(1 point)
CaCO3 CaO
CO2
112g
and 88g
C
a
O
C
O
2
40g
and 12g
C
a
O
C
O
2
56g
and 44g
C
a
O
C
O
2
200g
and 200g
C
a
O
C
O
2
Use the chemical equation to answer the question.
The molar mass of hydrogen (H) is 1g/mol, the molar mass of chlorine (Cl) is 35g/mol, and the molarmass of zinc (Zn) is 65g/mol. When 130g of zinc react completely in hydrochloric acid (HCl), how muchis the total mass of the products?
(1 point)
2HCl (ag) + Zn (s) → ZnCl2 (aq) + H2 (g)
130g
144g
270g
274g
Propane reacts with oxygen to produce carbon dioxide and water according to the following equation:
Which ratio of components is correct?
(1 point)
C3H8 + 5O2 → 3CO2 + 4H2O
For each mole of oxygen that reacts, 3 moles of carbon dioxide are produced.
For each mole of propane that reacts, 5 moles of oxygen are produced.
For every 4 moles of water produced, 3 moles of propane react.
For every 3 moles of carbon dioxide produced, 5 moles of oxygen react
Elements A and B react according to the following equation:
The molar mass of A is 12g/mol. The molar mass of B is 4g/mol. The molar mass of
is 28g/mol.When the goal of the reaction is to produce 112g of the product, how many grams of reactant A shouldbe present initially?
(1 point)
4A + B2 → 2A2B
A2B
16
24
48
96

A)
The molar mass of
is 110.98g/mol. How many molecules of
are there in 4g?
(1 point)
CaCl2 CaCl2
molecules
5.426
×
10
21
molecules
2.673
×
10
26
molecules
2.409
×
10
24
molecules
2.170
×
10
22

Answer 1

1) When the products are known, which fact can always be deduced about the reactants?
- Answer: the number of atoms in the reactants.
(By conservation of atoms: each element’s total number of atoms is the same on reactant and product sides.)

2) H2O2 → H2O + O2. Based on conservation of mass, which could be the product?
- Answer: 2 H2O2 → 2 H2O + O2.

3) CaCO3 → CaO + CO2. From 200 g CaCO3, possible masses of CaO and CO2?
- Answer: 112 g CaO and 88 g CO2.
(Molar masses: CaCO3 ≈100 g/mol → 2 mol ⇒ 2×56 =112 g CaO, 2×44 =88 g CO2.)

4) 2HCl + Zn → ZnCl2 + H2. If 130 g Zn reacts completely, total mass of products?
- Answer: 274 g.
(130 g Zn = 2 mol Zn; needs 4 mol HCl = 4×36 = 144 g; total mass = 130+144 = 274 g.)

5) C3H8 + 5O2 → 3CO2 + 4H2O. Which ratio is correct?
- Answer: For every 3 moles of carbon dioxide produced, 5 moles of oxygen react.

6) 4A + B2 → 2A2B. Molar masses: A =12 g/mol, B =4 g/mol, A2B =28 g/mol. To produce 112 g A2B, how many grams of A needed?
- Answer: 96 g of A.
(112 g /28 g/mol = 4 mol product. Reaction: 2 mol product requires 4 mol A, so 4 mol product requires 8 mol A → 8×12 =96 g.)

7) Molar mass CaCl2 = 110.98 g/mol. How many molecules in 4 g?
- Answer: 2.170 × 10^22 molecules.
(4 /110.98 mol × 6.022×10^23 ≈ 2.17×10^22.)