Virtual Chem-Lab:
Stoichiometry and Gas Law Simulations
Computer models, based upon the already established laws and theories, can help researchers to predict the outcome of an experiment in a much cheaper and efficient way than if he or she tried to run the same experiment in a lab. Often, a computer simulation will be run first, to determine if the experiment is viable. Once that is determined, and the scientist has an idea of what to expect, the actual experiment is run. The actual lab results are often similar to, but slightly different from the predicted model due to slight energy changes and real-world limitations (such as available equipment and human techniques).
Today in lab you will gain some experience using computer simulations as a tool to help you in two areas. In one simulation, you will practice your stoichiometry skills by running a model of a simple combustion reaction. This reaction occurs inside of a piece of machinery called a “bomb calorimeter”. This machine traps the reactants inside of a sealed, isolated container and is capable of measuring energy changes in addition to measuring the quantities and types of products formed.
In the second and third simulations, you will begin to work with gas laws, our next topic to be studied. You will work with the computer models to determine the relationships between temperature, pressure, and volume, and come to a conclusion about how these factors affect a gas.
Out with the Old… (stoichiometry simulation)
- Click on the tab labeled Step 1: Select Gas. Select CH4.
- Balance the equation at the top of the website and click submit. If correct, continue; if
not, fix it!
- Set the quantity of oxygen to 1.25 moles (or close to it)
- Set the quantity of methane to 2.00 moles (or close to it)
- Press the reaction button and gather the data in grams and moles.
- Write the balanced equation for the reaction you performed.
- Show the work for the stoichiometry that predicts the limiting reactant. What substance will be left over in the reactor?
- Use your limiting reactant to calculate the theoretical yield of the reaction.
- What was your percent yield? Is this a realistic value? Explain.
- Go back to step 1 on the simulation. Select a different gas and repeat the procedure and calculations for the new experiment.
In with the New… (gas law simulations)
- Select any gas from the gas menu.
- Drag the piston to any volume you like and let go.
- A data point will appear in the chart. Collect 10 data points.
- Graph the data points.
- Compare the Pressure vs Volume graph to the graph of 1/P vs Volume graph.
- Print and label both graphs. Attach all the graphs to this lab report.
- Is there a relationship between the pressure of the gas and the volume of the gas? What trends do you notice?
- Which graph (P vs V or 1/P vs V) best illustrates the relationship between pressure and volume? What makes you think so?
- Does it matter what gas you are dealing with? Go back and change the type of gas in the syringe. Collect another 10 data points and print the two graphs. What similarities and/or differences do you notice?
- Drag the temperature slider to the left until the temperature reads 273.15 Kelvin. Watch carefully to see what happens.
- Collect 9 more data points by sliding to different temperatures. Be sure to collect some high and some low temperatures.
- Click the button that will display the chart on the screen. Click the button that will plot the points. Print, label, and attach the graph.
- Is there a relationship between temperature of a gas and the volume of a gas? What trends do you notice?
- Do you think it matters what kind of gas you are dealing with? Explain why or why not.