Chemistry 2nd Semester Final Review

Combustion reactions are ones that always include elemental oxygen as a reactant. When a hydrocarbon (a substance made up of carbon and hydrogen) reacts with oxygen, the products of the combustion reaction are carbon dioxide and water.

Which products complete the reactants to form a balanced chemical equation for a combustion reaction?

2 C₂H₆ + 7 O₂ →

• 4 CO₂ + 6 H₂O

• 3 CO₂ + 6 H₂O

• 2 CO₂ + 8 H₂O

• 5 CO₂ + 4 H₂O

Answer explanation

Hydrogen, oxygen, and carbon each have the same number of atoms on both sides of the chemical equation.

What are the coefficients needed to balance this chemical reaction to show that matter is conserved?

Fe + Cl₂ → FeCl₃

• 1, 1, 1

• 2, 3, 2

• 3, 2, 2

• 4, 2, 2

Answer explanation

Using these coefficients gives 2 iron and 6 chlorine atoms on each side of the equation, demonstrating that matter is conserved.

This is the balanced chemical equation for the reaction that produces ammonia (NH₃) from nitrogen (N₂) and hydrogen (H₂).

N_2(g) + 3 H_2(g) → 2 NH_3(g)  

How many moles of ammonia (NH₃) would be produced if 2.5 moles of nitrogen (N₂) reacted with excess hydrogen (H₂)?

• 1.3 ml NH₃

• 2.5 mol NH₃

• 5.0 mol NH₃

• 7.5 mol NH₃

Answer explanation

This is the result of calculating moles of NH₃ using the 2:1 molar ratio 

Use the drop-down menus to complete the statement about this balanced chemical equation:

4 Al + 3 O₂ → 2 Al₂O₃

This balanced equation shows that ​ (a)   mole(s) of aluminum (Al) react with ​​ (b)   mole(s) of oxygen (O₂) to yield ​​ (c)   mole(s) of aluminum oxide (Al₂O₃). If a chemist wanted to produce 4 moles of aluminum oxide (Al₂O₃), she would need to start with ​​ (d)   moles of aluminum (Al) and ​​ (e)   moles of oxygen (O₂).

• 4
• 3
• 2
• 8
• 6

Answer explanation

This balanced equation shows that 4 mole(s) of aluminum (Al) react with 3 mole(s) of oxygen (O₂) to yield 2 mole(s) of aluminum oxide (Al₂O₃). If a chemist wanted to produce 4 moles of aluminum oxide (Al₂O₃), she would need to start with 8 moles of aluminum (Al) and 6 moles of oxygen (O₂).

Combustion reactions are ones that always include elemental oxygen as a reactant. When a hydrocarbon (substance made up of carbon and hydrogen) reacts with oxygen, the products of the combustion reaction are carbon dioxide and water.

Drag and drop the products to the correct reactants for these combustion reactions. The reactants have the correct coefficients for making balanced reactions.

CH₄ + 2 O₂→ ​ (a)  

2 C₂H₆ + 7 O₂→ ​ (b)  

C₃H₈ + 5 O₂→ ​ (c)  

• CO2 + 2 H2O
• 4 CO2 + 6 H2O
• 3 CO2 + 4 H2O

Aluminum metal (Al) reacts with hydrogen chloride (HCl) to produce aluminum chloride (AlCl₃) and hydrogen gas (H₂). Drag and drop the numbers into the boxes that balance the chemical equation for this reaction.

​ (a)   Al + ​ (b)   HCl → ​ (c)   AlCl₃ + ​ (d)   H₂

• 2
• 6
• 3
• 1
• 4
• 5
• 7
• 8

When hydrogen reacts with an element from group 5A, such as nitrogen, what is the coefficient needed for hydrogen in the chemical reaction shown in the picture?

• 1

• 2

• 3

• 4

Answer explanation

This coefficient causes the chemical equation to be balanced because there are 6 hydrogen atoms on each side of the chemical equation.

Which of the following has a greater mass?

one mole of gaseous carbon dioxide molecules (CO₂); or

one mole of frozen water molecules (H₂O

• H₂O

• CO₂

• The samples have the same weight

• There is not enough information to determine the answer

Silicon can react with oxygen to produce silicon dioxide.

Si + O₂ --> SiO₂

If 56 grams of silicon are consumed in this reaction, what mass of oxygen is reacted?

• 32 grams

• 128 grams

• 16 grams

• 64 grams

Answer explanation

The source of this information is http://www.ece.gatech.edu/research/labs/vc/theory/oxide.html

The mineral magnetite has the chemical formula Fe₃O₄. Which of these is closest to the molar mass of magnetite?

• 34 g/mol

• 72 g/mol

• 110 g/mol

• 232 g/mol

Answer explanation

The molar mass of magnetite (Fe₃O₄) is the sum of the atomic mass of iron times three and the atomic mass of oxygen times four: (55.85 x 3) + (16.00 x 4) = 231.55 ≈ 232