Chemical Reactions and Stoichiometry - SS1 Chemistry Past Questions and Answers - page 2
What is the coefficient of O2 when the following equation is balanced?
C3H8 + O2 → CO2 + H2O
2
3
4
5
Which of the following is a balanced equation for the combustion of propane (C3H8)?
C3H8 + 3O2 → 3CO2 + H2O
C3H8 + 5O2 → 3CO2 + 4H2O
C3H8 + 4O2 → 3CO2 + 4H2O
C3H8 + 2O2 → 3CO2 + 4H2O
What is the balanced equation for the reaction between calcium oxide (CaO) and water (H2O)?
CaO + H2O → Ca(OH)2
CaO + 2H2O → Ca(OH)2
CaO + H2O → CaH2O2
CaO + 3H2O → Ca(OH)3
What is the coefficient of Fe2O3 when the following equation is balanced?
Fe + O2 → Fe2O3
1
2
3
4
Explain the process of balancing chemical equations. Discuss the importance of balanced equations in understanding chemical reactions.
Balancing chemical equations is the process of adjusting the coefficients in front of the chemical formulas to ensure that the number of atoms of each element is the same on both sides of the equation. A balanced equation accurately represents the stoichiometry, or the quantitative relationship, between the reactants and products in a chemical reaction.
The process of balancing chemical equations involves the following steps:
- Identify the reactants and products in the chemical equation.
- Count the number of atoms of each element on both sides of the equation.
- Start by adjusting the coefficients of the compounds that contain the highest number of atoms of a particular element.
- Use trial and error to modify the coefficients until the number of atoms is balanced on both sides of the equation.
- Verify that the equation is balanced by counting the atoms of each element again.
Balanced equations are crucial for several reasons:
- Conservation of mass: Balancing equations ensures that the law of conservation of mass is obeyed. According to this law, the total mass of the reactants must be equal to the total mass of the products. Balanced equations show that the same number and types of atoms are present before and after the reaction, preserving mass.
- Stoichiometry: Balanced equations provide information about the mole-to-mole ratios between reactants and products. These ratios allow scientists to determine the amounts of substances involved in a reaction and predict the theoretical yield of products. It helps in understanding the quantitative aspects of a chemical reaction.
- Predicting reaction outcomes: Balanced equations help predict the products and their quantities in a reaction. By knowing the stoichiometry, scientists can determine the limiting reactant, which is the reactant that is completely consumed, and the excess reactant. This information aids in understanding the efficiency and yield of reactions.
In stoichiometry, the mole ratio is derived from:
Avogadro's number
The ideal gas law
The periodic table
The law of conservation of mass
The mole concept is based on the idea that:
All substances are made up of atoms
Chemical reactions occur in definite proportions
The number of particles can be counted using Avogadro's number
The mass of a substance can be determined using a balance
What is the relationship between the mole and Avogadro's number?
1 mole = 6.022 x 1023 particles
1 mole = 1.022 x 1023 particles
1 mole = 6.022 x 1024 particles
1 mole = 1.022 x 1024 particles
How many moles of oxygen are present in 4.8 grams of oxygen gas (O₂)? (Molar mass of O₂ = 32 g/mol)
0.15 moles
0.30 moles
0.60 moles
1.20 moles
The balanced equation for the reaction between hydrogen gas (H₂) and oxygen gas (O₂) to form water (H₂O) is:
H₂ + O₂ → H₂O
2H₂ + O₂ → 2H₂O
H₂ + 2O₂ → H₂O
2H₂ + 2O₂ → 2H₂O