Question

(a) Determine the chemical formula of the product formed when the metallic element calcium combines with the nonmetallic element oxygen, \(\mathrm{O}_{2}\). Write the balanced chemical equation for the reaction. (b) What products form when a compound containing \(\mathrm{C}, \mathrm{H}\), and \(\mathrm{O}\) is completely combusted in air? Write a balanced chemical equation for the combustion of acetone, \(\mathrm{C}_{3} \mathrm{H}_{6} \mathrm{O}(I)\), in air.

Short answer

(a) The chemical formula of the product formed when calcium combines with oxygen is calcium oxide, \(\mathrm{CaO}\). The balanced chemical equation for this reaction is: \[ \mathrm{2 Ca}(s) + \mathrm{O}_{2}(g) \rightarrow 2 \mathrm{CaO}(s) \] (b) When a compound containing carbon (C), hydrogen (H), and oxygen (O) is completely combusted in air, the products are carbon dioxide (\(\mathrm{CO}_{2}\)) and water (\(\mathrm{H}_{2}\mathrm{O}\)). The balanced chemical equation for the combustion of acetone, \(\mathrm{C}_{3} \mathrm{H}_{6} \mathrm{O}(I)\), in air is: \[ \mathrm{C}_{3}\mathrm{H}_{6}\mathrm{O}(I) + 4\,\mathrm{O}_{2}(g) \rightarrow 3\,\mathrm{CO}_{2}(g) + 3\,\mathrm{H}_{2}\mathrm{O}(g) \]

Step-by-step solution

(a) Determine the chemical formula

: Calcium (Ca) is in group 2 of the periodic table and has a valency of 2. Oxygen (O) is in group 16 and has a valency of 2 as well (since it needs 2 electrons to fill its outer shell). When calcium combines with oxygen, the resulting compound is calcium oxide, which has the chemical formula \(\mathrm{CaO}\). This is because each calcium atom donates 2 electrons, and each oxygen atom accepts 2 electrons, forming an ionic bond.

(a) Write the balanced chemical equation

: The balanced chemical equation for the reaction between calcium and oxygen is: \[ \mathrm{2 Ca}(s) + \mathrm{O}_{2}(g) \rightarrow 2 \mathrm{CaO}(s) \] This equation is balanced because there are the same number of each atom on both sides of the equation: 2 calcium atoms and 2 oxygen atoms.

(b) Determine the products of combustion

: For a compound containing carbon, hydrogen, and oxygen, when it is completely combusted in air, the products are carbon dioxide (\(\mathrm{CO}_{2}\)) and water (\(\mathrm{H}_{2}\mathrm{O}\)). This is because all the carbon atoms combine with oxygen to form carbon dioxide and all the hydrogen atoms combine with oxygen to form water.

(b) Write the balanced chemical equation for the combustion of acetone

: Acetone, \(\mathrm{C}_{3} \mathrm{H}_{6} \mathrm{O}(I)\), has the chemical formula \(\mathrm{C}_{3}\mathrm{H}_{6}\mathrm{O}\). When it is combusted in air (oxygen, \(\mathrm{O}_{2}\)), the products are carbon dioxide and water. The balanced chemical equation for the combustion of acetone is: \[ \mathrm{C}_{3}\mathrm{H}_{6}\mathrm{O}(I) + 4\,\mathrm{O}_{2}(g) \rightarrow 3\,\mathrm{CO}_{2}(g) + 3\,\mathrm{H}_{2}\mathrm{O}(g) \] This equation is balanced because there are the same number of each atom on both sides of the equation: 3 carbon atoms, 6 hydrogen atoms, and 6 oxygen atoms.

Key concepts

Chemical Formulas

Chemical formulas represent the elements in a compound and show the number of each type of atom present. The process of determining a chemical formula involves understanding the valency or combining power of the elements involved.
For instance, calcium (Ca) is a metal in Group 2 of the periodic table, which means it can lose 2 electrons.
Oxygen (O), on the other hand, is a nonmetal in Group 16, meaning it needs 2 electrons to fill its outer shell.
When these two elements react, calcium donates its 2 electrons to oxygen. As a result, calcium oxide with the formula \(\mathrm{CaO}\) is formed.

• The number and type of atoms involved form the basic skeleton of the chemical structure.
• These formulas allow scientists to predict the results of chemical reactions.

By understanding the chemical formula, you're able to decipher the composition and proportions of the chemicals involved.

Balancing Equations

Balancing chemical equations is an essential skill in chemistry. It ensures that the law of conservation of mass is adhered to, which states that matter cannot be created or destroyed. This means the atoms on the reactant side must equal the atoms on the product side of the equation.
To balance an equation, you adjust the coefficients (numerical values before a molecule) to ensure that the number of atoms for each element is equal on both sides.
Take the reaction between calcium and oxygen: \[ \mathrm{2 Ca(s) + O_{2}(g) \rightarrow 2 CaO(s)} \]
Here, both sides have:

• 2 calcium atoms
• 2 oxygen atoms
• The equation is balanced, providing a clear representation of what happens during the reaction.

Balancing chemical equations requires a bit of practice. Once mastered, it becomes an intuitive step in understanding chemical reactions.

Combustion Reactions

Combustion reactions are a type of reaction where a substance combines with oxygen to produce heat and light.
These reactions generally involve hydrocarbons and oxygen, resulting in carbon dioxide and water.
A common example of a combustion reaction is the burning of acetone in air. For acetone, which has a chemical formula \(\mathrm{C_{3}H_{6}O}\), the balanced combustion reaction is: \[ \mathrm{C_{3}H_{6}O(l) + 4 O_{2}(g) \rightarrow 3 CO_{2}(g) + 3 H_{2}O(g)} \]
This equation shows:

• 3 carbon atoms convert to 3 carbon dioxide molecules.
• 6 hydrogen atoms convert to 3 water molecules.
• Oxygen atoms are balanced across both sides.

Understanding combustion reactions is crucial for fields like energy production and environmental science. They illustrate how energy is released from chemical compounds and highlight the importance of oxygen in these processes.