Question

Consider the following equations. For each, decide whether it represents a chemical reaction or a physical change. (a) \(\mathrm{SnCl}_{4}(a q)+4 \mathrm{H}_{2} \mathrm{O}(l) \longrightarrow \mathrm{Sn}(\mathrm{OH})_{4}(s)+4 \mathrm{HCl}(a q)\) (b) \(4 \mathrm{~K}(s)+\mathrm{O}_{2}(g) \longrightarrow 2 \mathrm{~K}_{2} \mathrm{O}(s)\) (c) \(\mathrm{NaCl}(s) \longrightarrow \mathrm{Na}^{*}(a q)+\mathrm{Cl}^{-}(a q)\)

Short answer

a) Chemical Reaction, b) Chemical Reaction, c) Physical Change.

Step-by-step solution

Analyze Equation (a)

Look at the equation \(\mathrm{SnCl}_{4}(a q)+4 \mathrm{H}_{2} \mathrm{O}(l) \longrightarrow \mathrm{Sn}(\mathrm{OH})_{4}(s)+4 \mathrm{HCl}(a q)\). The reactants, which are initially different substances, react and form completely new substances. There is a rearrangement of atoms which suggests a chemical reaction.

Analyze Equation (b)

Consider the equation \(4 \mathrm{K}(s)+\mathrm{O}_{2}(g) \longrightarrow 2 \mathrm{K}_{2}\mathrm{O}(s)\). In this case, Solid Potassium and Oxygen gas react to form a new substance which is Potassium Oxide. The product created is a new molecule that wasn't present before. This suggests a chemical reaction.

Analyze Equation (c)

Now look at the equation \(\mathrm{NaCl}(s) \longrightarrow \mathrm{Na}^{*}(a q)+\mathrm{Cl}^{-}(a q)\). It represents a substance that, while undergoing a change, remains the same substance at the core. The Sodium Chloride (NaCl) dissociates into its ions but doesn't form new substances, which implies that this is a physical change.

Key concepts

Understanding Physical Change

A physical change occurs when a substance undergoes a change in one or more of its physical properties, such as its shape, phase, or size, without altering its chemical structure. Common examples include melting, freezing, dissolving, and cutting. The main thing to remember here is that, during a physical change, the molecular structure of the substance remains the same.
In the context of the provided exercise, consider the equation containing Sodium Chloride (\(\mathrm{NaCl}(s) \longrightarrow \mathrm{Na}^{+}(aq)+\mathrm{Cl}^{-}(aq)\)). This represents a process of dissolution. Here, solid NaCl dissolves in water and separates into its constituent ions, but it does not change its fundamental identity. The chemical makeup of NaCl remains intact. This indicates that the process is a physical change.
Key points of a physical change:

• No new substance is formed.
• The change is usually reversible.
• The chemical formula of the substance doesn't change.

Chemical Equation Basics

A chemical equation is a symbolic representation of a chemical reaction. It shows the reactants consuming and products forming, providing a clear structure of the transformation occurring. Chemical equations are written with the products on the right and reactants on the left, connected by an arrow pointing from reactants to products.
Each chemical species in the equation is represented by its chemical formula, and to adhere to the conservation of mass, chemical equations need to be balanced. This means the same number of each type of atom must be present on both sides of the equation.
When evaluating whether an equation represents a chemical reaction or not, consider the following:

• Are new substances formed?
• Is there a change in the configuration of atoms or molecules?
• Does the process produce energy or absorb it?

In our exercise, equations (a) and (b) represent chemical reactions, different from equation (c) which describes a physical change.

Exploring Reaction Analysis

Reaction analysis involves looking closely at the chemical equation to understand the process and its implications. This includes identifying the substances that react (reactants) and those that are produced (products) during the process.
Start by examining the reactants and products - look for changes in chemical composition, which indicate chemical reactions. For instance, in equation \(\mathrm{SnCl}_{4}(aq)+4 \mathrm{H}_{2} \mathrm{O}(l) \longrightarrow \mathrm{Sn}(OH)_{4}(s)+4 \mathrm{HCl}(aq)\), the products are chemically different from the reactants, signaling a transformation. Reaction analysis helps in understanding whether bonds are broken or formed.
While analyzing reactions, some questions to consider are:

• What new bonds are formed?
• What bonds are broken?
• What evidence can indicate such changes, like color change or temperature change?

By carefully analyzing these equations, we correctly differentiate between chemical reactions and physical changes.

The Process of Substance Transformation

Substance transformation is a central concept in understanding chemical reactions. During this process, the original substances (reactants) undergo a reorganization of atoms to form new substances (products). This reorganization involves breaking and forming of chemical bonds, accompanied by energy changes.
In chemical reactions, the transformation is significant as it alters the substances at the molecular level, producing entirely different substances. For instance, in equation \(4 \mathrm{K}(s)+\mathrm{O}_{2}(g) \longrightarrow 2 \mathrm{K}_{2} \mathrm{O}(s)\), Potassium and Oxygen combine to form a new substance, Potassium Oxide, exemplifying a transformation.
For an effective analysis, remember:

• Chemical bonds are crucial for understanding the transformation.
• A transformation results in new substances with different properties.
• The process often results in energy changes, such as heat being absorbed or released.

This transformation distinguishes chemical reactions from physical changes, where the substance retains its original composition.