Question

(a) What scientific principle or law is used in the process of balancing chemical equations? (b) In balancing equations, why should you not change subscripts in chemical formulas? (c) How would you write out liquid water, water vapor, aqueous sodium chloride, and solid sodium chloride in chemical equations?

Short answer

(a) The Law of Conservation of Mass is used for balancing chemical equations, ensuring that the number of atoms for each element in the reactants equals those in the products. (b) Changing subscripts alters the chemical identity of compounds, so only coefficients should be adjusted to balance equations. (c) Write the specific compounds as: liquid water - H₂O (l); water vapor - H₂O (g); aqueous sodium chloride - NaCl (aq); solid sodium chloride - NaCl (s).

Step-by-step solution

(a) Scientific Principle for Balancing Chemical Equations

The scientific principle or law used in the process of balancing chemical equations is the Law of Conservation of Mass. It states that mass cannot be created or destroyed in any ordinary chemical reaction. In other words, the total mass of the reactants should be equal to the total mass of the products, and the number of atoms of each element in the reactants should equal the number of atoms of those elements in the products.

(b) Reason to Not Change Subscripts

You should not change the subscripts in chemical formulas while balancing equations because doing so would alter the chemical identity of the compounds involved. Subscripts represent the exact ratio of atoms in a compound, and changing them would create a different compound altogether. To balance a chemical equation, alter only the coefficients, which indicate the number of molecules involved in the reaction without changing the compound's identity.

(c) Writing Specific Compounds in Chemical Equations

To write out specific compounds in chemical equations, use the following notations: 1. Liquid water: Use the symbol H₂O (l) for liquid water. The subscript "2" indicates that there are two hydrogen (H) atoms and one oxygen (O) atom in a water molecule, and the symbol (l) denotes the liquid state. 2. Water vapor: Use the symbol H₂O (g) for water vapor. Water vapor is water in its gaseous state, so the symbol (g) is used to represent it. 3. Aqueous sodium chloride: Use the symbol NaCl (aq) for aqueous sodium chloride. Aqueous means that sodium chloride is dissolved in water, and the chemical formula for sodium chloride is NaCl. The symbol (aq) denotes an aqueous solution. 4. Solid sodium chloride: Use the symbol NaCl (s) for solid sodium chloride. The symbol (s) denotes the solid state.

Key concepts

Law of Conservation of Mass

The Law of Conservation of Mass is a fundamental concept in chemistry that forms the basis for balancing chemical equations. This principle states that mass is neither created nor destroyed in an ordinary chemical reaction. In practical terms, this means that the total mass of reactants, or substances initially involved in the reaction, must be equal to the total mass of the products, which are substances formed by the reaction.

For students tackling chemistry problems, understanding this law is crucial. It implies that you must account for all atoms of each element when balancing a chemical equation. This is done by ensuring that the quantity of atoms for each element is the same on both sides of the equation. The process may involve adding coefficients, which are numbers placed before compounds that adjust the number of molecules without altering their identity. This meticulous process helps uphold the Law of Conservation of Mass and is vital in predicting the outcomes of chemical reactions.

Chemical Equation Notation

Chemical equation notation is the language through which chemists communicate the specifics of chemical reactions. A chemical equation uses chemical formulas to represent the reactants and products, and includes state symbols to indicate the physical state of each substance.

Understanding this notation involves recognizing several components:

• Chemical formulas: These represent the types and numbers of atoms in a molecule.
• Coefficients: These are numbers placed in front of chemical formulas to indicate the number of molecules or moles of a substance involved in the reaction.
• State symbols: These are written in parentheses after the chemical formulas and denote the physical state of the substance, such as (s) for solid, (l) for liquid, (g) for gas, and (aq) for aqueous solution.
• Plus signs (+): These indicate that substances are reactants or products in the reaction.
• Arrow (→): This separates the reactants from the products and shows the direction of the reaction.

By understanding and using these notations correctly, students can effectively describe and balance chemical reactions. It's also important to note that the equation should be balanced following the Law of Conservation of Mass, maintaining the correct stoichiometry of the reaction.

Subscripts in Chemical Formulas

Subscripts in chemical formulas play an integral role in conveying the composition of compounds. They are numbers written slightly below and to the right of atomic symbols in a chemical formula, indicating how many atoms of that element are present in a molecule. For example, in water (H₂O), the '2' is a subscript that tells us there are two hydrogen atoms for every one oxygen atom in a water molecule.

These subscripts are critical because they reflect the fixed ratio of atoms and define the unique characteristics of compounds. Changing a subscript value would change the compound's identity, which is why, in balancing chemical equations, you should never alter subscripts. Incorrectly modifying subscripts could suggest the creation or destruction of atoms, which would violate the Law of Conservation of Mass. Instead, to balance equations, adjust the coefficients, which are the numbers placed before the formulas that indicate the relative amounts of reactants and products without changing their identities.

Importance in Balancing Reactions

Subscripts serve as a guide to ensure that during the balancing process, the atom count for each element remains consistent. They also help in calculating the molecular weights and ultimately in determining the proportions of each substance required for a reaction. Correctly understanding and using subscripts is essential for students to grasp the intricacies of chemical reactions and to succeed in chemistry.