Grade 8
  1. Introduction to Chemistry  1.1. Nature and scope of chemistry  1.2. Importance of chemistry in daily life  1.3. Chemistry and its relation with other sciences  1.4. The role of chemistry in industry, medicine and the environment  1.5. Scientific investigation and experimental methods in chemistry
  2. Matter and its properties  2.1. Definition and classification of matter  2.2. Physical and chemical properties of matter  2.3. Law of conservation of matter  2.4. Extensive and Intensive Properties of Matter  2.5. Kinetic molecular theory of matter  2.6. States of matter: solids, liquids, gases, plasmas, and Bose-Einstein condensates  2.7. Changes in state and energy are involved  2.8. Diffusion and Brownian motion
  3. Elements, Compounds, and Mixtures  3.1. Definition and differences between elements, compounds, and mixtures  3.2. Atomic Structure and Atomic Number  3.3. Chemical symbols and formulas  3.4. Trends in the Periodic Table (Groups and Periods)  3.5. Classification of Elements: Metals, Nonmetals and Metalloids  3.6. Rare Earth Elements and Transition Metals  3.7. Types of mixtures: homogeneous and heterogeneous  3.8. Separation of Mixtures Using Physical and Chemical Methods
  4. Separation Techniques  4.1. Filtration, Sedimentation and Decantation  4.2. Evaporation and crystallization  4.3. Distillation and Fractional Distillation  4.4. Chromatography and its applications  4.5. Sublimation in the purification of compounds  4.6. The role of centrifugation in biochemical processes
  5. Atomic Structure  5.1. Dalton's atomic theory  5.2. Structure of the atom: protons, neutrons and electrons  5.3. Bohr's atomic model  5.4. Introduction to Quantum Mechanical Model  5.5. Electron Configuration and Energy Levels  5.6. Excitation and emission spectra  5.7. Isotopes and their applications
  6. Periodic Table and Chemical Trends  6.1. History and Development of the Periodic Table  6.2. Modern periodic law  6.3. Periodicity and trends in atomic and ionic sizes  6.4. Ionization Energy, Electron Affinity and Electronegativity  6.5. Introduction to Lanthanides and Actinides  6.6. Application of periodic trends in chemistry
  7. Chemical Bonding and Molecular Structure  7.1. Types of chemical bonds: ionic, covalent and metallic bonds  7.3. Polar and Nonpolar Molecules  7.4. Hydrogen bonding and its applications  7.5. Intermolecular forces: dipole-dipole, London dispersion force
  8. Chemical Reactions and Stoichiometry  8.1. Chemical Equations and Balance  8.2. Types of Chemical Reactions: Combination, Decomposition, Displacement and Redox  8.3. Introduction to stoichiometry and the mole concept  8.4. Limiting reactant in chemical equations  8.5. Reaction rate, catalyst, and factors affecting reaction rate
  9. Acids, Bases and Salts  9.1. Definition and Properties of Acids and Bases  9.2. Strong vs. Weak Acids and Bases  9.3. pH Scale and pH Calculation  9.4. Neutralization reactions  9.5. Buffer solutions and their importance  9.6. Applications of Acids, Bases and Salts in Daily Life
  10. Solutions and Solubility  10.1. Definition of Solution, Solute, and Solvent  10.2. Factors Affecting Solubility  10.3. Concentration units: molarity and molality  10.4. Saturated, unsaturated and supersaturated solutions  10.5. Concept of osmosis and reverse osmosis  10.6. Concentrative properties of solutions
  11. Gases and Gas Laws  11.1. Properties of gases  11.2. Introduction to Ideal and Real Gases  11.3. Boyle's Law, Charles' Law and Avogadro's Law  11.4. Ideal Gas Equation and Its Applications  11.5. Application of Gas Laws in Real Life
  12. Thermochemistry and energy transformation  12.1. Energy in Chemical Reactions  12.2. Exothermic vs. Endothermic Reactions  12.3. Heat and Enthalpy Changes  12.4. Calorimetry and heat transfer in reactions
  13. Metals and Nonmetals  13.1. Physical and Chemical Properties of Metals and Nonmetals  13.2. Reactivity Series of Metals  13.3. Corrosion and its prevention  13.4. Extraction of metals from ores  13.5. Uses of metals and non-metals in daily life
  14. Introduction to Organic Chemistry  14.1. Characteristics of carbon and organic compounds  14.2. Functional groups and their importance  14.3. Simple Hydrocarbons: Alkenes, Alkenes and Alkynes  14.4. Isomerism in organic compounds  14.5. Introduction to polymers and their uses
  15. Environmental Chemistry and Sustainability  15.1. Green Chemistry Principles  15.2. Effects of Chemical Pollution on Ecosystems  15.3. Acid rain and its effects  15.4. Ozone layer depletion and global warming  15.5. Waste Management and Recycling in Chemistry

Grade 8 → Chemical Reactions and Stoichiometry ↓


Limiting reactant in chemical equations


In chemistry, reactions are often depicted with balanced chemical equations. In these reactions, the substances we start with are called reactants, and the substances that are formed are called products. When we have a chemical reaction, the amount of reactants will determine how many products can be formed. Understanding which reactant will limit the amount of product generated helps us predict the course of a chemical reaction.

What is the limiting reactant?

The limiting reactant in a chemical reaction is the substance that is used up first. When this reactant is completely used up, the reaction stops, even if other reactants are still present. This concept is important because it determines how much product can be formed in a reaction.

Let's consider a simple analogy: Imagine you are baking cookies. If you have 10 cups of flour, 5 cups of sugar, and 2 eggs, but the recipe calls for 1 egg, 2 cups of flour, and 1 cup of sugar for each batch of cookies, the number of eggs will limit how many batches you can bake. You will run out of eggs first, even if you have plenty of flour and sugar. Similarly, in a chemical reaction, the limiting reactant is the substance that restricts the formation of more products.

Chemical equations and stoichiometry

Before diving into limiting reactants, it's important to understand how chemical equations work. A balanced chemical equation shows the relationship between reactants and products in terms of their molecules or moles. Balancing a chemical equation requires that there be the same number of atoms of each element on both sides of the equation.

For example, consider the combustion of methane:

CH4   2O2 → CO2   2H2O

In this equation, 1 molecule of methane (CH4) reacts with 2 molecules of oxygen (O2) to form 1 molecule of carbon dioxide (CO2) and 2 molecules of water (H2O).

Identifying the limiting reactant

To identify the limiting reactant in a chemical reaction we follow these steps:

  1. Balance the chemical equation.
  2. Convert all given reactant quantities (usually in grams or liters) to moles.
  3. Use stoichiometry to determine the mole ratio in a balanced equation.
  4. Calculate the amount of product formed from each reactant.
  5. The reactant that produces the least amount of product is the limiting reactant.

A visual example: the reaction of hydrogen and oxygen

Let us illustrate this concept with a simple example of the reaction between hydrogen and oxygen to produce water:

2H2   O2 → 2H2O

Imagine you have 4 molecules of hydrogen (H2) and 3 molecules of oxygen (O2).

According to the balanced chemical equation, 2 molecules of H2 react with 1 molecule of O2 to form 2 molecules of H2O

With 4 H2 (which means we can make 4/2 = 2 batches of water) and 3 O2 (which means we can make 3 batches of water), hydrogen is the limiting reactant because it can make fewer batches. Thus, when hydrogen is completely used up only 2 molecules of H2O are formed.

Numerical example: iron and sulfur reaction

Consider the reaction between iron and sulfur to form iron(II) sulfide:

8Fe   S8 → 8FeS

Imagine you have 32 grams of iron and 16 grams of sulfur. First, convert the mass of each reactant to moles:

  • Atomic mass of Fe (iron) = 55.85 g/mol
  • Atomic mass of S (sulphur, S8 molecules) = 256.48 g/mol (32.06 g/mol for one atom)

Convert grams to moles:

Moles of Fe = 32 g / 55.85 g/mol ≈ 0.573 moles
Moles of S8 = 16 g / 256.48 g/mol ≈ 0.0624 moles

This balanced chemical equation implies:

  • 8 moles of Fe react with 1 mole of S8 to form 8 moles of FeS

Determine how many moles of FeS can be produced from each reactant:

0.573 moles of Fe will make 0.573 moles of FeS
0.0624 moles of S8 will make 8 * 0.0624 = 0.499 moles of FeS

Sulfur is the limiting reactant because it produces less (0.499) moles of FeS.

Conclusion

Identifying the limiting reactant helps to accurately predict the amount of product formed in a chemical reaction. In each case, the reactant that forms the smallest amount of product determines the extent of the reaction. Mastering this concept in chemistry is fundamental because it can affect how we perform experiments and industrial chemical processes, saving time and resources.

Understanding limiting reactants involves combining knowledge about chemical equations, stoichiometry, and logical problem-solving. With practice, this concept becomes intuitive and a powerful tool for anyone studying chemistry.


Grade 8 → 8.4


U
username
0%
completed in Grade 8

← Prev (8.3)
Introduction to stoichiometry and the mole concept
Next (8.5) →
Reaction rate, catalyst, and factors affecting reaction rate

Comments 



Limiting reactant in chemical equations

https://www.chemistryelite.com/g8/8.4?ceal=en