Imagine you and your friends are making hot dogs. A complete hot dog consists of a wiener and a bun. At the store, you buy four packages of eight wieners and three bags of 10 buns.

Student Exploration: Limiting Reactants

Vocabulary: chemical equation, chemical formula, chemical reaction, coefficient, limiting reactant, molecule, product, reactant, subscript

Prior Knowledge Questions (Do these BEFORE using the Gizmo.)

Imagine you and your friends are making hot dogs. A complete hot dog consists of a wiener and a bun. At the store, you buy four packages of eight wieners and three bags of 10 buns.

How many total hot dogs can you make? ______________________________________

Which ingredient limited the number of hot dogs you could make? __ _________­___

Which ingredient will you have leftovers of? ____________________ _________

Gizmo Warm-up

Just as ingredients can be put together to make a new food, substances can combine during a chemical reaction to produce new substances. The substances that undergo change are called reactants. The new substances are products.

Sometimes during a chemical reaction, one type of reactant will be used up before the other reactants. This reactant is the limiting reactant. Using the Limiting Reactants Gizmo™, you can determine which reactant is limiting in various scenarios.

To begin, make sure H2 + O2 becomes H2O is selected. The small “2” in H2, O2, and H2O is a subscript. Subscripts represent the number of atoms in a molecule.

Use the sliders to set the number of O2 molecules and H2 molecules to two.

How many hydrogen molecules (H2) are there? _______ Hydrogen atoms? _______

How many oxygen molecules (O2) are there? _______  Oxygen atoms? ___

How many H2O molecules do you think will form when these four molecules react? ______

Click Play (). How many H2O molecules actually formed? _____ 

Activity A: Water reaction

Get the Gizmo ready: Make sure H2 + O2 becomes H2O is selected. Click Reset ().

Goal: Identify a limiting reactant.

Count: H2O is the chemical formula for water. In order to produce a single molecule of water, how many hydrogen atoms are needed? _______  Oxygen atoms? _______

Predict: Set the number of O2 molecules to five and the number of H2 molecules to eight.

How many oxygen atoms are present? ___Hydrogen atoms? _______

How many water molecules could form from these reactants? _______

After the molecules react, which reactant will be left over? _______ ______

Which reactant will be the limiting reactant? ___________ ____

Click Play and wait until Reaction complete is shown. What happened? _________ _____________ _____________________________

Test: Click Reset.Set the number of O2 molecules to 10.

How many hydrogen molecules (H2) will be needed for there to be no excess reactants? ______ Use the slider to set the number of H2 molecules to this value.

How many water molecules will be formed? _______

Click Play. What happened?

Challenge yourself: Run the Gizmo with five O2 molecules and nine H2 molecule

How many of each molecule do you think will be produced by this reaction?

O2: _______                   H2: _______                           H2O: _______

Click Play. How many were actually produced? O2: _____ H2: _____ H2O: ____

How do you explain this result? _______ ___

Activity B: Methane reaction

Get the Gizmo ready: Select C + H2 becomes CH4.

Goal: Predict the results of a chemical reaction.

Count: CH4 is the chemical formula for methane. In order to produce a single molecule of methane, how many carbon (C) atoms are needed? _______ Hydrogen atoms? _______

Predict: Set the number of C atoms to 14 and the number of H2 molecules to 10.

How many total hydrogen atoms are there? _______

How many methane molecules could form from these reactants? _______

After the atoms react, which reactant will be left over? ________

Which reactant will be the limiting reactant? __ _____________

Click Play and wait until Reaction complete is shown. What happened?

Test: Click Reset.Set the number of C atoms to seven.

How many hydrogen molecules (H2) will be needed for there to be no excess reactants? _____ Use the slider to set the number of H2 molecules to this value.

How many methane molecules will be formed? _______

Click Play. What happened?.

Solve: For each chemical equation below, write the number of product molecules that will form from the reaction. Then, circle the limiting reactant. (Note: The coefficients in front of the reactants indicate the number of reactant molecules or atoms present.)

5C + 6O2 à _______ CO2

4Na + 8Cl2 à ___NaCl

3CO2 + 4H2O à _______ H2CO3

7N2 + 9H2 à _______ NH3

10Zn + 16HCl à _______ ZnCl2 + _______ H2