Question

For each chemical equation (which may or may not be balanced), list the number of each type of atom on each side of the equation, and determine if the equation is balanced. (a) \(\mathrm{MgS}(a q)+2 \mathrm{CuCl}_{2}(a q) \longrightarrow 2 \mathrm{CuS}(s)+\mathrm{MgCl}_{2}(a q)\) (b) \(2 \mathrm{C}_{6} \mathrm{H}_{14}(l)+19 \mathrm{O}_{2}(g) \longrightarrow 12 \mathrm{CO}_{2}(g)+14 \mathrm{H}_{2} \mathrm{O}(g)\)

Short answer

Equation (a) is not balanced; there are different numbers of S atoms on either side of the equation. Equation (b) is balanced; each type of atom has the same number on both sides of the equation.

Step-by-step solution

Identify atoms in equation (a)

For equation (a), identify the number of Mg, S, Cu, and Cl atoms in the reactants and products.

Count atoms for equation (a)

On the left (reactants) side of equation (a), there is 1 Mg atom, 1 S atom, 2 Cu atoms, and 4 Cl atoms (from the 2 coefficients in front of CuCl2). On the right (products) side, there are 2 Cu atoms, 2 S atoms, 1 Mg atom, and 2 Cl atoms (from the 1 coefficient in front of MgCl2).

Determine if equation (a) is balanced

Compare the count of each type of atom on both sides of equation (a). The numbers of Mg, Cu, and Cl atoms are balanced, but S is not. There are 1 S atom on the reactant side and 2 S atoms on the product side.

Identify atoms in equation (b)

For equation (b), identify the number of C, H, and O atoms in the reactants and products.

Count atoms for equation (b)

On the left (reactants) side of equation (b), there are 12 C atoms (from 2 coefficients times 6 from the C6), 28 H atoms (from 2 coefficients times 14 from the H14), and 38 O atoms (from the 19 coefficients in front of O2). On the right (products) side, there are 12 C atoms (from the 12 coefficients in front of CO2), 28 H atoms (from the 14 H2O with each containing 2 H atoms), and 38 O atoms (from the 12 CO2 with each containing 2 O atoms, and 14 H2O with each containing 1 O atom).

Determine if equation (b) is balanced

Compare the count of each type of atom on both sides of equation (b). The numbers of C, H, and O atoms are balanced on both sides with 12, 28, and 38 atoms respectively.

Key concepts

Stoichiometry

Stoichiometry is akin to the 'recipe' of chemistry; it's the part of chemistry that relates to measuring and calculating the quantities of reactants and products in a chemical reaction. It's fundamental to ensuring a reaction goes to completion and that none of the reactants are wasted. This concept also ensures that chemical equations are properly balanced, reflecting the law of conservation of mass which states that matter cannot be created or destroyed in a closed system.

When we talk about stoichiometry in the context of chemical equations, we refer to the coefficients in front of each compound. These coefficients represent the relative number of mole units of each substance involved in the reaction. They ensure that the same number of atoms of each element is present both before and after the reaction, upholding the law of conservation of mass.

Importance in Chemical Reactions

In practice, stoichiometry allows scientists and engineers to predict the amount of products formed from a given amount of reactants and, conversely, the amount of reactants needed to create a desired quantity of product. This is invaluable in industries ranging from pharmaceuticals to manufacturing, where precise chemical composition is crucial.

Chemical Reactions

A chemical reaction is a process that leads to the transformation of one set of chemical substances into another. Reactants are transformed into products through the breaking and forming of chemical bonds. There are various types of chemical reactions, including synthesis, decomposition, single displacement, double displacement, and combustion, each with unique characteristics.

Reaction Mechanism

Underlying every chemical reaction is a mechanism that describes the step-by-step process by which reactants become products. This mechanism provides insight into which bonds break, which bonds form, and the order in which these events occur. Understanding the mechanism is essential for controlling the rate and outcome of a reaction.

Role of Energy

Energy changes are also a core part of chemical reactions. Reactions can be either exothermic, releasing heat, or endothermic, absorbing heat. The energy required to initiate a reaction is known as the activation energy, and the study of energy changes during reactions falls under the field of thermochemistry.

Atom Counting

Atom counting is a fundamental skill in balancing chemical equations, which lies at the heart of both stoichiometry and understanding chemical reactions. To balance a chemical equation, every atom on the reactant side must be accounted for on the product side.

It begins with listing each element present in the reaction and tallying the number of atoms of each element on both sides of the equation. Discrepancies in these numbers indicate that the equation is unbalanced and adjustments must be made to the coefficients of the reactants and/or products to achieve balance.

Significance in Chemical Equilibrium

Atom counting is not just important for the equations' balance; it also plays a key role in chemical equilibrium. In reversible reactions, the correct atom count helps to establish the relationship between the amounts of reactants and products at equilibrium. Understanding how to count atoms quickly and efficiently enables students and chemists to assess reaction progress, calculate yields, and predict how changes in conditions could shift the reaction.