Download Name: Period:______ Let`s make some sandwiches! Introduction: If

Name:______________________
Period:_________
Let’s make some sandwiches!
Introduction:
If a sandwich shop runs out of bread, the shop closes down. No more sandwiches can be fully made
without ordering more bread from a bakery. A similar thing happens in a chemical reaction. If there are
fixed amounts of reactants to work with in a chemical reaction, one of the reactants may be used up
first. This prevents the production of more products. In this activity, you will look at several situations
where the process or reaction is stopped because one of the required components has been used up.
Procedure: Go to Phet Simulation: Reactants, Products, and Leftovers
(http://phet.colorado.edu/en/simulation/reactants-products-and-leftovers) and click Run Now!
Part 1: Making Sandwiches (click on Sandwich Shop tab on top left)
1. The Cheese Sandwich is a simulation of a two reactant synthesis reaction.
2. Set the cheese sandwich formula to 2 bread slices and 1 cheese slice.
3. Complete the table below while making tasty cheese sandwiches:
Trial
Bread (reactant)
Cheese (reactant)
Sandwiches (product) Leftovers (bread)
1
5 slices
5 slices
2
4 slices
3 slices
3
2 sandwiches
2 slices
4
6 slices
3 sandwiches
5
8 slices
0 slices
Record 3 Observations for this simulation
What do you notice about those numbers when there are no “leftovers”? (Hint: ratios)
Explain why you couldn’t make 3 sandwiches in Trial #3?
Part 2: Real Chemical Reactions (click on the real reaction tab on top)
1. Now let’s work with real chemical reactions.
2. What is the mole ratio for the reaction of hydrogen and oxygen to produce water?
__ H 2  __ O2  __ H 2O
3. Complete the table below while making water from hydrogen H2 and O2:
Leftovers(cheese)
0 slices
4 slices
0 slices
Trial #
Hydrogen
Molecules H2
Oxygen
Molecules O2
1
4 molecules
4 molecules
2
3
7 molecules
10 moles
6 molecules
5 moles
4
9 moles
8 moles
5
6
8 moles
4 moles
6 moles
7 moles
Water
Molecules
H2O
Excess H2
Excess O2
4. Notice that the labels changed from molecules to moles. This does not change the mole ratio,
as a mole is simply a large number of molecules. How many molecules are in a mole?
5. In Trial #6, what reactant limits you from making more water molecules? Which reactant was
present in excess and remained after the production of water was complete?
6. For each trial, circle the reactant that limits the quantity of water produced--this is the limiting
reactant.
7. Looking back at your table, is the reactant with the smallest number of moles always the limiting
reactant? Explain your reasoning.
8. Calculate the number of moles of H2 needed to react with 13 moles of O2.
9. If 18 moles of H2 reacted with 22 moles of O2, determine:
a. What is the maximum number of moles of H2O that can be produced?
b. How many moles of H2 are left in excess after the reaction (if any)?
c. How many moles of O2 are left in excess after the reaction (if any)?
d. Which reactant is the Limiting Reactant?
10. In reality, reactants don’t have to react in perfect whole numbers of moles. In a two-reactant
synthesis reaction, usually one reactant gets entirely used up (and determines how much
product is made), even if that means using fractions of a mole of reactant. For instance, if 15
moles of H2 reacted with 11 moles of O2, all 15 moles of H2 would react, with only 7.5 moles of
O2 (2:1 mole ratio). This would produce only 15 moles of H2O, leaving 14.5 moles of excess O2
behind.
11. Now assume 25.5 moles of H2 and 11 moles of O2 react:
a. Which reactant is the Limiting Reactant?
b. Which reactant must be the Excess Reactant?
c. How much (in moles) of water gets produced? (Show Work)
d. If all the limiting reactant gets used up, how much of the excess reactant is left? (Show
Work)