Consider the following equations. For each, decide whether it represents a chemical reaction or a physical change.
a. SnCl4(aq) + 4H2O(l) Sn(OH)4(s) + 4HCl(aq)
b. 4K(s) + O2(g) 2K2O(s)
c. NaCl(s) Na+(aq) + Cl-(aq)
If the products are different from the reactants you have a chemical change; otherwise it's a physical change.
a. The equation represents a chemical reaction. It is a precipitation reaction where the reactants react to form a precipitate (Sn(OH)4) and aqueous products (HCl).
b. The equation represents a chemical reaction. It is a synthesis reaction where potassium (K) reacts with oxygen (O2) to form potassium oxide (K2O).
c. The equation represents a physical change. It is a dissolution or dissociation process where solid sodium chloride (NaCl) dissolves in water to form aqueous sodium ions (Na+) and chloride ions (Cl-).
To determine whether each equation represents a chemical reaction or a physical change, we need to understand the difference between the two.
A chemical reaction involves the rearrangement of atoms to form new substances with different properties. In contrast, a physical change involves a change in the physical state or form of a substance, but no new substances are formed.
Now let's analyze each equation:
a. SnCl4(aq) + 4H2O(l) → Sn(OH)4(s) + 4HCl(aq)
In this equation, we see the formation of a solid Sn(OH)4 and the production of hydrochloric acid (HCl) in the aqueous state. Since new substances are formed with different properties, this equation represents a chemical reaction.
b. 4K(s) + O2(g) → 2K2O(s)
In this equation, elemental potassium (K) reacts with oxygen gas (O2) to form potassium oxide (K2O). New substances are formed, indicating a chemical reaction.
c. NaCl(s) → Na+(aq) + Cl-(aq)
In this equation, solid sodium chloride (NaCl) dissociates into sodium ions (Na+) and chloride ions (Cl-) in the aqueous state. Although there is a change in the state of the substance, no new substances are formed. Therefore, this equation represents a physical change.
To summarize:
a. Chemical reaction
b. Chemical reaction
c. Physical change