# Lesson Worksheet: Balancing Chemical Equations Chemistry • 7th Grade

In this worksheet, we will practice determining the stoichiometry of a reaction equation by balancing the numbers of atoms in the reactants and products.

**Q3: **

The Marsh test is a method used historically for the detection of arsenic, a toxic element, in mixed materials. The sample is burned to convert any arsenic present to arsenic(III) trioxide and then treated with nitric acid and metallic zinc. If arsenic is present, a garlic smell is detected due to the production of arsine gas . The equation for this reaction is as follows:

The coefficients , , , and are all whole numbers.

Find the value of .

Find the value of .

Find the value of .

Find the value of .

**Q4: **

The reaction of selenium, selenium tetrachloride , and aluminum trichloride produces a compound with the molecular formula , according to the following equation:

Find the value of .

Find the value of .

Find the value of .

**Q5: **

Complete combustion reactions are described by the following equation:

In this equation, , , and are whole numbers or simple fractions. The compound is a single molecule of an organic fuel. Possible organic fuels include butanol , catechol , and cyclopentene .

Place the listed organic fuels in order of increasing values of .

- ACatechol, butanol, cyclopentene
- BButanol, catechol, cyclopentene
- CCyclopentene, catechol, butanol
- DCyclopentene, butanol, catechol
- EButanol, cyclopentene, catechol

Place the listed organic fuels in order of increasing values of .

- ACatechol, butanol, cyclopentene
- BButanol, cyclopentene, catechol
- CCyclopentene, catechol, butanol
- DCyclopentene, butanol, catechol
- ECatechol, cyclopentene, butanol

Place the listed organic fuels in order of increasing values of .

- AButanol, cyclopentene, catechol
- BCatechol, butanol, cyclopentene
- CCyclopentene, butanol, catechol
- DButanol, catechol, cyclopentene
- ECatechol, cyclopentene, butanol

**Q6: **

Sodium azide reacts with nitrous acid to produce nitric oxide , sodium hydroxide , and nitrogen gas. This reaction is described by the following equation:

The coefficients , , , and are whole numbers or simple fractions.

In which order are the coefficients , , , and most easily determined?

- A, ,,
- B, ,,
- C, ,,
- D, ,,
- E, ,,

When the coefficient of is set to a value of 1, as shown, which coefficients are also equal to 1?

- A, ,
- B,
- C, ,,
- D, ,
- E,

**Q7: **

The black mineral magnetite reacts with high-temperature oxygen to form red-brown ferric oxide . This reaction is described by the following equation:

The coefficients , , and are whole numbers and may be determined by balancing the numbers of and atoms on the two sides of the equation.

When balancing the equation, which of the two elements should be considered first? why?

- A, because fewer reactants and products contain atoms or ions of this element
- B, because fewer atoms of this element appear in the equation
- C, because all reactants and products contain atoms or ions of this element
- D, because more atoms of this element appear in the equation
- E, because it appears in the equation as a pure element

What are the smallest possible whole-number values of , , and ?

- A, ,
- B, ,
- C, ,
- D, ,
- E, ,

**Q9: **

Antimony(III) oxide is a white solid used as a flame retardant additive in some plastics. The compound may be produced by the oxidation of antimony(III) sulfide in a high-temperature furnace. The equation for this reaction is as follows:

The coefficients , , and are whole numbers and may be determined by balancing the numbers of , , and atoms on the two sides of the equation.

In which order are the coefficients , , and most easily determined?

- A, ,
- B, ,
- C, ,
- D, ,
- E, ,

What are the values of , , and ?

- A, ,
- B, ,
- C, ,
- D, ,
- E, ,