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The mole ratio is the ratio of two compounds that are involved, in the balanced reaction. A balanced reaction is essential to understand the ratio in which the molecules are needed to complete a given reaction.
- It cannot be done with an unbalanced reaction as the exact ratio of reactant and product will not be known.
- The mole ratio can be used to compare the product formed when certain moles of product are used for the reaction.
- The concept of stoichiometry is used to understand the chemistry involved in a chemical reaction. The mole ratio is dimensionless.
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Key Terms: Mole, mole ratio, balanced reaction, stoichiometry, chemical reaction, dimensionless
What is a mole?
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The amount of substance that has exactly 6.02214076 x 1023 entities of a given substance is called a mole. This specific number is called as Avagadro constant and is denoted by the symbol NA. 1 mole of every atom or molecule will have the same number of molecules that is the Avagadro. For example:
- 1 mole of ammonia molecule means 6.02214076 x 1023 molecules.
- 1 mole of sodium ions means 6.02214076 x 1023 sodium ions.
Read more: Difference Between An Atom And A Molecule
Weight of 1 mole
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The mass of one mole of an element is equal to the atomic mass (in grams) of the element. For any substance, it is equal to the molecule mass of that substance. For example, the mass of a 1-mole hydrogen molecule is 2g and that of a hydrogen atom is 1 g.
What is the mole ratio?
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A mole ratio is defined as the ratio of two compounds, that are involved in a balanced reaction. A balanced reaction is used so that a comparison of ratios can be done. These ratios give the estimation of the molecules that are necessary for the completion of a chemical reaction.
Read more: Chemical Reaction
Unit of a mole ratio
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The mole ratio depicts the mole: mole ratio of the given elements involved in the reaction. It is dimensionless.
How to determine the mole ratio?
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To balance a chemical reaction, the concept of stoichiometry is used, and then calculate the number of products and reactants. A chemical reaction depends mainly on the amount of substance (reactants) present. Therefore, mole ratios cannot be calculated with the help of an unbalanced reaction.
For example: N2 + 3H2 → 2NH3
The above reaction is a balanced reaction, the coefficients of N2, H2, and NH3 are 1, 3, and 2 respectively. This means that 1 mole of N2 and 3 moles of H2 are needed to produce 2 moles of NH3.
So, now the calculation of the mole ratio can be done as given below:
- Mole ratio between H2 and NH3 = (3 mole of H2/ 2 mole of NH3 ) = 3:2
- Mole ratio between NH3 and H2= (2 mole of NH3 / 3 mole of H2) = 2:3
- Mole ratio between N2 and H2= (1 mole of N2 / 3 mole of H2) = 1:3
The mole ratio determines the amount of substance that is required in a chemical reaction. It is the ratio of any two compounds that are involved in the reaction. The reaction should be balanced to get the correct mole ratio. It is dimensionless as it is a mole: mole ratio.
Read Further: Difference Between Molar mass and Molecular mass
Things to Remember
- The mole ratio is the ratio of moles of any two compounds that are involved in a chemical reaction.
- The mole ratio determines the amount of substance that is required in a chemical reaction.
- The unit of mole ratio is dimensionless.
- To calculate the mole ratio, the reaction should be balanced.
- 1 mole of an atom or molecule is equal to 6.02214076 x 1023.
- 6.02214076 x 1023 is called Avagadro’s number
Previous Year Questions
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Sample Questions
Ques: What are the types of chemical reactions? (2 marks)
Ans: A chemical reaction can be classified into six types:
Ques: How to balance a chemical reaction? (3 marks)
Ans: The rules that have to be followed while balancing a chemical reaction is as follows:
- The formula of all the molecules involved in the chemical reaction should be correct.
- Balance one molecule at a time.
- The big numbers need to be changed according to the molecule.
Example: N2 + H2 → NH3
After balancing the above equation, it will become N2 + 3H2→ 2NH3
Ques: Define mole ratio. (1 mark)
Ans: The ratio of two compounds that are involved in a chemical reaction is called the mole ratio. The reaction needs to be balanced. The unit of mole ratio is dimensionless.
Ques: Find the mole ratio of H2 and H2O in 2H2 + O2 → 2H2O (2 marks)
Ans: Here the coefficients H2 of =2
- The coefficients of O2= 1
- The coefficients of H2O = 2
Therefore, the mole ratio will be 2 mole/2 mole. That is 2:2
Ques: What is the importance of the mole ratio? (2 marks)
Ans: The mole ratio, helps in the comparison of molecules that are required to complete a chemical reaction. This will tell the amount of reactants that should be added in order to get the desired product.
Ques: Consider the chlorination reaction of methane (CH4): CH4(g) + 4Cl2(g) → CCl4(g) + 4HCl(g) (2 marks)
How many moles of CH₄ were used in the reaction if 51.9 g of CCl4 were obtained?
Ans: Moles of CCl4 by molar mass:
CCl4 = 51.9g × \(\frac{1}{153.8}\)=0.337mol
Now, moles of CH4, the ratio is 1:1 therefore, it will be 0.337mol
Ques: Find the number of particles in 0.01 moles of Na. (2 marks)
Ans: 1 mole of Na will have 6.02214076 x 1023 particles.
Therefore, 0.01 moles of Na will have 6.02214076 x 1023 × 0.01 particles.
Ques: Find the mole ratio of the compounds in 2NO₂ → 2NO + O2. (3 marks)
Ans: The above-given reaction is a balanced chemical reaction. Make sure that the reaction is balanced.
The mole ratio of NO2 and NO is 2:2 that is 1:1
The mole ratio of NO and O2 is 2:1
The mole ratio of O2 and NO2 is 1:2
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