BALANCING CHEMICAL EQUATIONS Load the simulation Balancing Chemical Equations http://phet.colorado.edu/en/simulation/balancing-chemical-equations CRITICAL THINKING QUESTIONS 1. Explore the Balancing Chemical Equations simulation. Discuss with your group what you find. a) What are the different ways that the simulation indicates when an equation is balanced? 2. For each balanced reaction, indicate the total number of molecules in the table below. Reaction Total Number of Molecules Reactant Side Product Side (Left) (Right) Make Ammonia Separate Water Combust Methane 3. Is the number of total molecules on the left side of a balanced equation always equal to the number of total molecules on the right side of the equation? Explain your answer. 4. For each balanced reaction, indicate the total number of atoms in the table below. Reaction Total Number of Atoms Reactant Side Product Side (Left) (Right) Make Ammonia Separate Water Combust Methane
The Correct Answer and Explanation is:
Ways to Indicate a Balanced Equation in the Simulation:
The simulation typically shows when an equation is balanced by:
- Color indicators: When the equation is balanced, the atoms (represented by balls of different colors) on both sides of the equation will match in terms of quantity and type. For example, if the left side has 3 red balls (representing hydrogen atoms), the right side will also have 3 red balls.
- Numerical Indicators: The simulation may display numbers above or beside each element to indicate how many molecules of each substance are involved in the reaction. These numbers will be equal on both sides when balanced.
- Visual Alignment: The shapes or models in the simulation will align visually when the equation is balanced, ensuring the number of atoms in the reactants equals that in the products.
2. Total Number of Molecules in Different Reactions:
To answer this, you will need to load the simulation and identify the specific reactions mentioned (Make Ammonia, Separate Water, Combust Methane). However, here’s a general guide:
- Make Ammonia (NH₃): The balanced equation is usually N₂ + 3H₂ → 2NH₃.
- Reactant side: 1 molecule of N₂ and 3 molecules of H₂.
- Product side: 2 molecules of NH₃.
- Total molecules on the left = 1 + 3 = 4, Total molecules on the right = 2.
- Separate Water (2H₂O → 2H₂ + O₂):
- Reactant side: 2 molecules of H₂O.
- Product side: 2 molecules of H₂ and 1 molecule of O₂.
- Total molecules on the left = 2, Total molecules on the right = 3.
- Combust Methane (CH₄ + 2O₂ → CO₂ + 2H₂O):
- Reactant side: 1 molecule of CH₄ and 2 molecules of O₂.
- Product side: 1 molecule of CO₂ and 2 molecules of H₂O.
- Total molecules on the left = 3, Total molecules on the right = 3.
3. Is the Number of Total Molecules Always Equal on Both Sides of the Equation?
No, the total number of molecules on the left side of a balanced equation may not always equal the total number of molecules on the right side. The law of conservation of mass states that the number of atoms is conserved in a chemical reaction, but the number of molecules may differ. This is because molecules on the reactant side can combine or break apart into different numbers of molecules on the product side. For example:
- In the combustion of methane, the reactant side may have fewer molecules than the product side, but the total number of atoms is the same.
4. Total Number of Atoms in Different Reactions:
Similarly, you can use the simulation to identify the exact number of atoms involved in each reaction. Here’s a general explanation:
- Make Ammonia (N₂ + 3H₂ → 2NH₃):
- Left: 2 nitrogen atoms (N₂) and 6 hydrogen atoms (3H₂).
- Right: 2 nitrogen atoms (2NH₃) and 6 hydrogen atoms (2NH₃).
- Separate Water (2H₂O → 2H₂ + O₂):
- Left: 4 hydrogen atoms (2H₂O) and 2 oxygen atoms.
- Right: 4 hydrogen atoms (2H₂) and 2 oxygen atoms (O₂).
- Combust Methane (CH₄ + 2O₂ → CO₂ + 2H₂O):
- Left: 1 carbon atom (CH₄), 4 hydrogen atoms (CH₄), and 4 oxygen atoms (2O₂).
- Right: 1 carbon atom (CO₂), 4 hydrogen atoms (2H₂O), and 2 oxygen atoms (CO₂ + H₂O).
Explanation:
When balancing chemical equations, it’s essential to ensure that the number of atoms for each element on the left (reactants) matches the number on the right (products). This aligns with the law of conservation of mass, which states that matter cannot be created or destroyed in a chemical reaction.
In some reactions, like combustion, the number of molecules can differ between the reactant and product sides. For example, the combustion of methane (CH₄) involves one molecule of methane reacting with two molecules of oxygen to form carbon dioxide and water. While the number of molecules changes (reactants = 3, products = 3), the number of atoms stays constant. This is because the atoms in the reactants simply rearrange to form the products.
The simulation helps visualize these changes by representing atoms as colored balls. The number of these balls on each side should be equal for a balanced equation, even if the number of molecules changes. For example, in the reaction for separating water, two molecules of water break down into hydrogen and oxygen, but the total number of atoms remains the same. In the case of ammonia synthesis, the ratio of nitrogen to hydrogen is essential to balance the equation correctly.
Understanding the balance of molecules and atoms in these reactions is fundamental in chemical reactions, where the number of atoms before and after the reaction remains unchanged, ensuring that mass is conserved.
