Work through four sections: recognise the type of each reaction, balance equations by adjusting coefficients until every atom is conserved, calculate the theoretical and percent yield of a reaction, and determine empirical and molecular formulae from composition data.
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Theory — Reaction Types, Balancing, and Yield
Types of Chemical Reaction
Most reactions fall into a few recognisable patterns. Identifying the type often helps you predict the products and balance the equation.
Type
Pattern
Example
Synthesis (combination)
A + B → AB
N₂ + 3H₂ → 2NH₃
Decomposition
AB → A + B
2KClO₃ → 2KCl + 3O₂
Single replacement
A + BC → AC + B
2K + MgBr₂ → 2KBr + Mg
Double replacement
AB + CD → AD + CB
FeCl₃ + 3NaOH → Fe(OH)₃ + 3NaCl
Combustion
fuel + O₂ → CO₂ + H₂O
CH₄ + 2O₂ → CO₂ + 2H₂O
Neutralisation
acid + base → salt + water
HCl + NaOH → NaCl + H₂O
Balancing Equations
A balanced equation has the same number of each atom on both sides — mass is conserved. Balance using coefficients only; never change subscripts. Treat polyatomic ions (such as NO₃⁻ and SO₄²⁻) as units where possible, and remember the diatomic elements H₂, O₂, N₂, F₂, Cl₂, Br₂, I₂.
Adjust coefficients only until every element matches
Theoretical and Percent Yield
The theoretical yield is the maximum product predicted by the balanced equation from the amounts of reactant used. The percent yield compares what was actually obtained to that maximum.
Yield
moles of reactant = mass ÷ molar mass
moles of product = moles of reactant × (mole ratio from equation)
theoretical yield = moles of product × molar mass of product
percent yield = (actual yield ÷ theoretical yield) × 100 %
Percent yield is normally less than 100 % in a real experiment
Conservation of Mass
Atoms are not created or destroyed; coefficients make both sides equal.
Empirical vs Molecular
Empirical formula is the simplest whole-number ratio; the molecular formula is a whole-number multiple of it.
Percent Yield
Actual ÷ theoretical × 100. A real reaction usually gives less than 100 %.
Apparatus
The equipment a real equation-balancing experiment uses. In the simulation these are modelled for you, but the readings correspond to what each instrument would measure.
Molecular model kit
Shows atoms are conserved, so equations must balance.
Analytical balance
Demonstrates conservation of mass in a reaction.
Reagent bottles
Hold the reactant solutions for the demonstrations.
Reaction flask
Where the reactants combine to form products.
Periodic table chart
Gives the formulas and charges needed to write equations.
Beaker
Mixes and observes the reacting solutions.
Instructions — Running the Virtual Experiment
The simulation has three sections. Complete each one and record your results, with screenshots, in your lab report.
Part 1 — Reaction Types (Reaction Types tab)
1
Open Simulation → Reaction Types. For each reaction shown, choose the type (synthesis, decomposition, single replacement, double replacement, or combustion) and check your answer.
2
Record at least five reactions with their correct types in your report.
Part 2 — Balancing (Balancing tab)
1
Open Balancing. For each skeleton equation, type whole-number coefficients. The atom tally shows the count of each element on both sides.
2
Adjust coefficients until every element matches in the lowest whole-number ratio, then click Check. Record at least three balanced equations with a screenshot.
Part 3 — Percent Yield (Yield tab)
1
Open Yield. Select a reaction and one of its three reactant sets (each set uses amounts that react together completely). Predict the mass of product, then click Calculate yield to see the theoretical yield.
2
Enter the actual yield obtained and record the reactant amounts, theoretical yield, actual yield, and percent yield for at least two cases.
Open Empirical & Molecular. In Part A, choose a percent composition and work out the mole ratio yourself, then click Find empirical formula to check. Record the moles of each element, the simplest whole-number ratio, and the empirical formula.
2
In Part B, enter the molar mass and click Find molecular formula. Record n = molar mass ÷ empirical-formula mass and the resulting molecular formula for at least two compounds.
Simulation — Balancing Chemical Reactions
Balancing Virtual LabRecognise · Balance · Yield
N₂ + 3 H₂ → 2 NH₃
Reaction
Reaction 1 of 10
Score
Correct0
Attempted0
Choose the pattern that matches the reactants and products.
Choose a reaction and one of its three reactant sets. Each set uses amounts that react together completely. Predict the yield yourself first, then click Calculate yield to check.
Reaction
Reactant amounts
Reactant amounts
N₂14.01 g
H₂3.02 g
Predict the product mass, then click Calculate yield.
Yield result
ProductNH₃
Theoretical yield17.03 g
Actual yield14.5 g
Percent yield85.1 %
Percent yield = actual ÷ theoretical × 100.
Enter a percent composition, then find the empirical formula
Part A — Empirical formula
Part B — Molecular formula
Uses the empirical formula from Part A. n = molar mass ÷ empirical-formula mass.
Result
Empirical formula—
Empirical mass— g/mol
n = M ÷ emp. mass—
Molecular formula—
Find the empirical formula first, then the molecular formula.
Team Questions
Question 1. What type of reaction is 2KClO₃ → 2KCl + 3O₂? (synthesis, decomposition, single replacement, double replacement, or combustion)
Question 2. Balance: __ H₂ + __ O₂ → __ H₂O. Type the three coefficients (e.g. 2,1,2).
Question 3. Balance: __ C₃H₈ + __ O₂ → __ CO₂ + __ H₂O. Type the four coefficients (e.g. 1,5,3,4).
Question 4. What type of reaction is CH₄ + 2O₂ → CO₂ + 2H₂O? (Type the type)
Question 5. A reaction has a theoretical yield of 17.0 g and an actual yield of 14.5 g. What is the percent yield? (Type to 1 decimal, e.g. 85.3)
Question 6. A compound has empirical formula CH₂O and a molar mass of 180 g/mol. The empirical formula mass is 30 g/mol. What is the molecular formula? (Type it, e.g. C6H12O6)
Question 7 — Challenge. When balancing, are you allowed to change a subscript to make the atoms balance? (yes or no)
Example Lab Report
Sample report demonstrating the expected format. Include labelled screenshots of each section, and your balanced equations for every reaction you completed.
To recognise the major types of chemical reaction, to balance chemical equations by conservation of mass, and to calculate the theoretical and percent yield of a reaction.
Method
Using the virtual lab, reactions were first classified by type, then balanced by adjusting coefficients until the atom tally matched on both sides, and finally analysed for yield by choosing a reactant set and comparing the actual yield with the theoretical yield. Screenshots were taken of each section.
Reactions were correctly classified into synthesis, decomposition, single and double replacement, and combustion. All equations were balanced by conservation of mass using coefficients only. The percent yield of ammonia was 85.2 %, less than 100 % as expected for a real process where some product is lost or the reaction does not go to completion.
Practice Questions
Show all work. Balance with coefficients only; remember the diatomic elements and keep polyatomic ions together.
