Question

Write the unbalanced equations for the following reactions: (a) Propane reacts with oxygen to form carbon dioxide and water. (b) Sodium metal is added to water and the products are sodium hydroxide and hydrogen gas.

Short answer

Unbalanced reactions: (a) C3H8 + O2 -> CO2 + H2O, (b) Na + H2O -> NaOH + H2.

Step-by-step solution

Writing the Unbalanced Equation for Propane Combustion

Start by writing the chemical formula for propane, which is C3H8. Next, indicate that it reacts with oxygen, which is O2. The products of the combustion of a hydrocarbon like propane are carbon dioxide (CO2) and water (H2O). The unbalanced equation is: C3H8 + O2 -> CO2 + H2O.

Writing the Unbalanced Equation for Sodium Reaction with Water

Write the chemical symbol for sodium, which is Na. Then write the chemical formula for water, H2O. The products of the reaction between sodium and water are sodium hydroxide (NaOH) and hydrogen gas (H2). The unbalanced equation is: Na + H2O -> NaOH + H2.

Key concepts

Propane Combustion

Understanding the basics of propane combustion is crucial for students learning about chemical reactions. Propane, a hydrocarbon, reacts vigorously with oxygen in a combustion reaction. Propane's chemical formula is represented as \( C_3H_8 \). Combustion reactions always involve oxygen (represented as \( O_2 \) in balanced equations) and result in the formation of carbon dioxide (\( CO_2 \) and water (\( H_2O \) as products. The significance lies in the conversion of chemical energy into heat and light energy, which is why propane is used as a fuel.

When writing the unbalanced chemical equation, we start with the reactants: propane and oxygen, and then we list the products, carbon dioxide and water, without initially worrying about the number of atoms of each element. This step lays the foundation for balancing the equation, which is a crucial part of understanding stoichiometry. To visualize the reaction, consider a barbecue grill where propane gas burns, combining with the atmosphere's oxygen to provide the heat needed to cook food.

Sodium Reaction with Water

The reaction of sodium with water is another exciting display of chemical interaction, often demonstrated in classrooms for its vigorous behavior. Sodium (\( Na \) is a highly reactive metal that, when in contact with water (\( H_2O \), results in a strong exothermic reaction. The products of this reaction are sodium hydroxide (\( NaOH \) and hydrogen gas (\( H_2 \).

The equation is started by writing the chemical symbols for the reactants and products. Here, understanding chemical formulae is pivotal, as it allows students to grasp the identities of reactants and products involved. The process of balancing this reaction helps students appreciate the laws of conservation of mass and charges – no atom is lost or gained, merely rearranged into new compounds. Due to its reactivity with water, sodium is stored under oil or in a dry, inert atmosphere to prevent accidental reactions.

Chemical Formulae

A firm grasp of chemical formulae is essential for students to accurately engage with chemistry. Chemical formulae are shorthand representations of molecules and compounds, indicating the types and numbers of atoms involved. For instance, the chemical formula \( C_3H_8 \) for propane tells us that each molecule comprises three carbon atoms and eight hydrogen atoms.

Moreover, understanding the formulae allows for the prediction of reaction products. For example, knowing that a hydrocarbon like propane will produce \( CO_2 \) and \( H_2O \) upon combustion becomes intuitive with solid knowledge of chemical formulae. Similarly, recognizing that sodium metal reacting with water produces \( NaOH \) and \( H_2 \) is part of this understanding. Consistency in the use of chemical formulae enables scientists and students alike to communicate complex chemical concepts succinctly and accurately.

Stoichiometry

Finally, stoichiometry is the branch of chemistry that deals with the quantitative relationships between reactants and products in a chemical reaction. It is the counting of atoms to satisfy the Law of Conservation of Mass, which states that matter can neither be created nor destroyed. After writing the unbalanced equations for the propane combustion and the sodium reaction with water, the next vital step is to balance the equations.

For correct stoichiometry, each element must have the same number of atoms on both sides of the equation. This might involve adding coefficients in front of the chemical formulas to balance the number of atoms. For example, the full stoichiometric equation of propane combustion involves balancing carbon, hydrogen, and oxygen atoms, so the end result reflects the exact proportions needed for the combustion reaction to occur. This practice supports the prediction of amounts of reactants required or products formed, crucial for everything from cooking recipes to industrial processes.