Engineers and Environmental Challenges

Engineers today are dealing with many environmental problems. These include pollution, waste management, and finding new ways to produce energy that is good for the planet. One useful tool for engineers is stoichiometry. This involves calculating how much of each chemical is needed in a reaction.

Let’s look at a few examples showing how engineers use stoichiometry to help the environment.

1. Reducing Air Pollution

Air pollution is a major issue, especially from factories and cars. Engineers can use stoichiometry to improve how fuel burns in power plants and vehicles.

Example Problem:

If a power plant uses 1000 kg of coal, how much carbon dioxide ($\text{CO}_2$) do they create?

When burning coal, the basic reaction is: $\text{C} + \text{O}_2 \rightarrow \text{CO}_2$

From stoichiometry, one unit of carbon makes one unit of carbon dioxide.

To figure out how much $\text{CO}_2$ is made:

1. First, convert coal weight to moles.

   • There are about 12 grams in one mole of carbon.
   • 1000 kg = 1,000,000 g
   • Moles of C = 1,000,000 g ÷ 12 g/mol = about 83,333 mol

2. Now, calculate how much $\text{CO}_2$ is produced.

   • 1 mole of C makes 1 mole of $\text{CO}_2$.
   • Since each mole of $\text{CO}_2$ weighs about 44 grams:
   • Amount of $\text{CO}_2$ produced = 83,333 mol × 44 g/mol = about 3,666,667 g, or 3666.67 kg.

This shows how engineers predict pollution produced when generating energy.

2. Treating Wastewater

Another important challenge is cleaning wastewater. Engineers need to find the right amount of chemicals to remove harmful materials from water. Stoichiometry helps them figure this out.

Example Problem:

Suppose a treatment plant processes 5000 liters of water containing 3 mg of phosphate ($\text{PO}_4^{3-}$) per liter.

To find out how much aluminum sulfate ($\text{Al}_2(\text{SO}_4)_3$) is needed to remove it:

1. First, calculate the total phosphate:

   • Total $\text{PO}_4^{3-}$ = 3 mg/L × 5000 L = 15,000 mg = 15 g.

2. Now, convert grams to moles:

   • Moles of $\text{PO}_4^{3-}$ = 15 g ÷ 94.97 g/mol = about 0.158 mol.

3. Find out how much aluminum sulfate is required:

   • The reaction tells us that 6 moles of $\text{PO}_4^{3-}$ need 2 moles of aluminum sulfate.
   • Moles of $\text{Al}_2(\text{SO}_4)_3$ = 0.158 mol × (2/6) = about 0.0527 mol.

4. Convert moles back to grams:

   • Mass of $\text{Al}_2(\text{SO}_4)_3$ = 0.0527 mol × 342.15 g/mol = about 18.01 g.

This process shows how stoichiometry helps engineers clean wastewater efficiently.

3. Creating Renewable Energy

With the search for renewable energy like biofuels, engineers can also use stoichiometry to improve how these fuels are made.

Example Problem:

In making biodiesel from triglycerides and methanol, the reaction looks like this: $\text{Triglycerides} + 3\text{CH}_3\text{OH} \rightarrow \text{Glycerol} + 3 \text{Biodiesel}$

If an engineer wants to convert 1000 g of triglyceride to biodiesel, how much methanol do they need?

1. First, calculate moles of triglycerides:

   • Molar mass is about 900 g/mol.
   • Moles of triglycerides = 1000 g ÷ 900 g/mol = about 1.11 mol.

2. Find moles of methanol needed:

   • Each mole of triglyceride needs 3 moles of methanol.
   • Moles of $\text{CH}_3\text{OH}$ = 1.11 mol × 3 = about 3.33 mol.

3. Convert methanol moles to grams:

   • Mass of $\text{CH}_3\text{OH}$ = 3.33 mol × 32.04 g/mol = about 106.79 g.

This helps engineers create fuel sources that are better for the environment.

4. Carbon Capture and Storage

With climate change becoming a bigger problem, engineers are looking at ways to capture carbon dioxide ($\text{CO}_2$) from the air. Stoichiometry is important for calculating how much carbon can be stored.

Example Problem:

When $\text{CO}_2$ reacts with calcium hydroxide ($\text{Ca(OH)}_2$), it creates calcium carbonate ($\text{CaCO}_3$): $\text{CO}_2 + \text{Ca(OH)}_2 \rightarrow \text{CaCO}_3 + \text{H}_2\text{O}$

If an engineer wants to capture 100 tons of $\text{CO}_2$, how much calcium hydroxide do they need?

1. Convert tons to grams:

   • 100 tons = 100,000 kg = 100,000,000 g.

2. Calculate moles of $\text{CO}_2$:

   • Moles of $\text{CO}_2$ = 100,000,000 g ÷ 44.01 g/mol = about 2,272,673.66 mol.

3. From the equation, 1 mole of $\text{CO}_2$ needs 1 mole of $\text{Ca(OH)}_2$:

   • Moles of $\text{Ca(OH)}_2$ = 2,272,673.66 mol.

4. Convert moles to grams:

   • Molar mass of $\text{Ca(OH)}_2$ is about 74.10 g/mol.
   • Mass of $\text{Ca(OH)}_2$ = 2,272,673.66 mol × 74.10 g/mol = about 168,281,929.4 g, or 168.28 tons.

This shows how much is needed for carbon capture.

5. Making Sustainable Materials

When creating biodegradable materials, engineers use stoichiometry to make sure that what’s left over is safe for the environment.

Example Problem:

For example, making polylactic acid (PLA) from lactic acid looks like this: $n \text{C}_3\text{H}_6\text{O}_3 \rightarrow \text{(C}_3\text{H}_4\text{O}_2\text{)}_n + n \text{H}_2\text{O}$

If an engineer starts with 100 g of lactic acid, how much PLA can they create?

1. Calculate moles of lactic acid:

   • The molar mass is about 90.08 g/mol.
   • Moles of lactic acid = 100 g ÷ 90.08 g/mol = about 1.11 mol.

2. Assuming each lactic acid molecule gives one PLA molecule, the mass of PLA is:

   • Mass of PLA = 1.11 mol × 72.06 g/mol = about 80.00 g.

This helps engineers design materials that are better for the environment.

Conclusion

Stoichiometry is a valuable tool for engineers. It helps them understand chemical processes that are important for tackling environmental challenges. From cutting down fuel emissions to cleaning wastewater and developing sustainable materials, stoichiometric calculations support many practical solutions for a healthier planet.

As new problems arise, engineers will continue to use stoichiometry to find ways that reduce negative impacts on our environment and promote sustainability.