Table I.

Experiment	Reactant1 (R)	Reactant2 (GB)
Exp #1 (Java) Exp #1 (movie)	4	4

NOTE: If you the simulation does not load (you see an X) after clicking the link above go to http://java.com/en/ and follow the instructions. We will be using these types of simulations many times this semester and next. You may also view the Exp#1 as a movie, if the Java Applet does not load.

Briefly describe what you observed happening in the reaction container Before and then After clicking on the Enable Reaction button. (NOTE: Use words like molecules atoms, collision, velocity, reaction, reactants and products.)

Before clicking on the Enable Reaction button there are four GB molecules and four R atoms moving around in the container colliding with each other and the walls of the container. The particles appear to have different velocities that change when colliding with another particle. When the Enable Reaction button is clicked a reaction occurs between the GB molecule and the R atom when the R atom collides with the GB molecule at the G side of the molecule. The products formed are an RG molecule and a B atom. The reaction continues until all four GB molecules and R atom collide correctly to form four RG molecules and four B atoms.

Table II for Experiment #1 has been completed with all the information. It is important to note that the row labeled 'Initial Amount' is completed before the Enable Reaction button is clicked, that the row labeled 'Final Amount' is completed after the reaction has gone to completion, and finally the row labeled 'Change Amount' can be completed last. It is essential to note that the it is only the 'Change Amount' row that adheres to the stoichiometry indicated by the coefficients in the balanced chemical equation. That neither the 'Initial Amount' row or the 'Final Amount' row adhere to the stoichiometry indicated by the coefficients in the balanced chemical equation.

To summarize what happens in the simulation for Exp #1 look at Table II. which has been completed as an example.

Table II: Experiment #1.

	REACTANTS	REACTANTS		PRODUCTS	PRODUCTS
Exp. #1	Reactant(1)	Reactant(2)		Product(1)	Product(2)
Formula	R	BG	--->	RG	B
Initial Amount	4	4		0	0
Change Amount	-4	-4		+4	+4
Final Amount	0	0		4	4

How many Red atoms were present initially?

There are four Red atoms initially in the container.

How many Red atoms reacted?

All four Red atoms react. Enough time must be allowed for the reaction to go to completion.

How many RG molecules were formed?

Four RG molecules are produced.

Now perform Experiment #2 - #3: To access each experiment click the mouse on the Exp # link below. This will open a new window containing a reaction container. Complete Table II for Exp#2 and #3 in the same way as Table II for Exp #1 above.

Experiment	Reactant1 (R)	Reactant2 (GB)
Exp #2 (Java) Exp #2 (movie)	4	2
Exp #3 (Java) Exp #3 (movie)	2	4

 

Reminder Instructions: Enter the formula for each reactant (recommend using the capitalized first letter for the color(s) of the particle as it formula, for example R and BG) and the initial amount of each reactant in Table II: Experiment #2 or #3. After recording this information for the particular experiment (#2 or #3) in the appropriate table, click on the Resume Button and then click on the Enable Reaction button and then observe what takes place in the reaction container. After the reaction is 'complete' enter the formula(s) of the product(s) of the reaction in the table. Also enter the final amounts of the reactants and the product(s) in the table.

 

Table II: Experiment #2

	REACTANTS	REACTANTS		PRODUCTS	PRODUCTS
Exp. #2	Reactant(1)	Reactant(2)		Product(1)	Product(2)
Formula	R	GB	--->	RG	B
Initial Amount	4	2		0	0
Change Amount	-2	-2		+2	+2
Final Amount	2	0		2	2

Table II: Experiment #3.

	REACTANTS	REACTANTS		PRODUCTS	PRODUCTS
Exp. #3	Reactant(1)	Reactant(2)		Product(1)	Product(2)
Formula	R	GB	--->	RG	B
Initial Amount	2	4		0	0
Change Amount	-2	-2		+2	+2
Final Amount	0	2		2	2

 

Write a balanced chemical equation describing the reaction you observed in each experiment. (Use a format similar to R1 + R2 --> P1 + P2 when writing the equation for the reactions observed. Use a single space to separate reactants, products, plus sign and the reaction arrow.)

Exp. #1:

The equation for the reaction is R + GB ---> RG + B

Exp. #2:

The equation for the reaction is R + GB ---> RG + B

Exp. #3:

The equation for the reaction is R + GB ---> RG + B

It is important to note that the chemical equation that describes the reaction that occurs is the same each time. A balanced equation never depends on the amounts of the reactants or products. A balanced chemical equation only tells us the ratio which reactants combine and form products.

A reagent in excess is a reactant that is not completely used up in a chemical reaction, a limiting reagent is a reactant that limits the amount of product formed in a chemical reaction. Look back at Table II Exp#1, #2 and #3 and select one of the radioboxes below that best fits the assignment of the excess reagent and the limiting reagent.

In Exp #1: (do as a group radiobutton)

R is the excess reagent and GB is the limiting reagent:

GB is the excess reagent and R is the limiting reagent:

both R and GB are excess reagents:

both R and GB are limiting reagents

In Experiment #1 since both reactants completely reacted and there are no particles of either reactant remaining after the reaction is complete, there cannot be an excess reagent. So both reactants are limiting. This will happen anytime there is a stoichiometrically related amount of both reactants.

In Exp #2:

R is the excess reagent and GB is the limiting reagent:

GB is the excess reagent and R is the limiting reagent:

both R and GB are excess reagents:

both R and GB are limiting reagents

In Experiment #2 since R and BG react in one to one ratio, and there is more R initially than GB, R is in excess and GB is the limiting reagent. Note it is important to remember that it is a combination of the coefficients associated with each reactant and the initial amount that must be used to determine the reactant that is excess and the limiting reactant.

In Exp #3:

R is the excess reagent and GB is the limiting reagent:

GB is the excss reagent and R is the limiting reagent:

both R and GB are excess reagents:

both R and GB are limiting reagents

In Experiment #3 since R and BG react in a one to one ratio, and there is more GB initially than R, GB is in excess and R is the limiting reagent. Note it is important to remember that it is a combination of the coefficients associated with each reactant and the initial amount that must be used to determine the reactant that is excess and the limiting reactant.

Consider the figure below representing a chemical reaction between H₂(g) and O₂(g) forming H₂O(g)

Which reactant, H₂(g), O₂(g), neither or both, is/are the limiting reagent?

The limiting reagent in the figure is H₂(g).

Explain:

Looking at the product container there are two O₂(g) molecules remaining unreacted. Therefore O₂(g) is in excess in the reaction, so H₂(g) is the limiting reagent.

Write the balanced chemical equation that represents the reaction that occurs in the figure.

2H₂(g) + O₂(g) --> 2H₂O(g)

Remember the coefficients in the balanced chemical equation reflect the ratio that the reacts combine.