Problem 9 - Chemistry: The Central Science

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 one write out liquid water, water vapor, aqueous sodium chloride, and solid sodium chloride in chemical equations?

Step-by-Step Solution

Answer

(a) The scientific principle used in balancing chemical equations is the Law of Conservation of Mass, which ensures the number of atoms of each element is conserved. (b) Changing subscripts in chemical formulas would alter the chemical nature of the substance, so we only adjust coefficients. (c) Symbols for different states are: liquid water - H_2O(l); water vapor - H_2O(g); aqueous sodium chloride - NaCl(aq); solid sodium chloride - NaCl(s).

Step 1: (a) Scientific Principle or Law

The scientific principle or law used in the process of balancing chemical equations is the Law of Conservation of Mass. According to this law, the mass of reactants in a chemical reaction must be equal to the mass of products, which implies that the number of atoms of each element must be conserved.

Step 2: (b) Reason for not changing Subscripts

Subscripts in chemical formulas represent the relative proportions of atoms in the molecule. Changing subscripts would alter the chemical nature of the substance, leading to a different compound. Balancing equations involves only adjusting the coefficients (the numbers in front of the chemical formulas), which do not affect the identity of the substance, but rather indicate the amounts of each reactant and product involved in the reaction.

Step 3: (c) Writing Symbols for Water and Sodium Chloride

To represent water in its different states and sodium chloride in its different states in a chemical equation, we use the following notations: 1. Liquid water: H_2O(l) 2. Water vapor: H_2O(g) 3. Aqueous sodium chloride: NaCl(aq) 4. Solid sodium chloride: NaCl(s)

Key Concepts

Law of Conservation of Mass

In chemistry, the Law of Conservation of Mass is a fundamental principle. It plays a crucial role in balancing chemical equations. This law states that mass is neither created nor destroyed in a chemical reaction. Instead, it is conserved. This means the total mass of reactants before the reaction must equal the total mass of products after the reaction takes place. When balancing chemical equations, it's essential to ensure that the number of atoms for each element in the reactants matches the number in the products. This ensures that no mass is lost or gained, adhering to the conservation of mass. In other words, whatever matter you start with, you must end up having it albeit reconfigured into new substances.

Chemical Formulas

Chemical formulas are a compact way of expressing information about the atoms in a compound. Each element in a compound is represented by its chemical symbol, and subscripts are used to show the number of each type of atom in the compound. Subscripts should never be changed when balancing chemical equations. They indicate the specific number of atoms in a molecule. If they were altered, it would change the actual substance, resulting in a different compound. Instead, we use coefficients in front of the chemical formulas when balancing equations. Coefficients adjust the quantities of the substances involved but leave their identities intact.

Chemical States Notation

In chemical equations, each compound can exist in different states. These states are denoted through symbols in parentheses right after the chemical formula. This notation helps in understanding the conditions under which a reaction takes place. For instance:

• Liquid Water: This is written as \( \text{H}_2\text{O}(l) \) where \((l)\) denotes liquid state.
• Water Vapor: Represented as \( \text{H}_2\text{O}(g) \), with \((g)\) indicating gaseous state.
• Aqueous Sodium Chloride: Denoted by \( \text{NaCl}(aq) \), where \((aq)\) signifies that the compound is dissolved in water.
• Solid Sodium Chloride: Written as \( \text{NaCl}(s) \), with \((s)\) indicating solid state.

Chemical states notation provides insight into the physical conditions of a chemical species, which can affect the progression and outcome of a chemical reaction.