Stoichiometry

Stoichiometry

By Mihir Paranjape

BCA Tables

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​BCA tables are means to calculate stoichiometry of a reaction.

We need a BALANCED reaction to do a BCA table.

BCA table is always in terms of Moles.​ So have to convert to moles.

B - Before: What is given.

C - Change: Reactants is -, Products is +, linked by mole ratio

A - After: B+C​

Limiting and Excess Reagents

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​This refers to REACTANTS only.

Limiting reagent is the reactant that RUNS OUT in a reaction.

Excess reagent is still LEFT OVER after the reaction.

You can use the BCA table to determine what remains and what runs out.​

BCA Tables

e.g. what would 6 moles of NaHCO₃ yield?​

​ 2 NaHCO₃ → Na₂CO₃ + CO₂ + H₂O

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​	​NaHCo3	​Na2CO3	​CO2	​H2O
​B	​6	​0	​0	​0
​MR	​	​	​	​
​C (basisxR)	​	​	​	​
​A	​	​	​	​

BCA Tables

Consider reaction: N₂ + 3H₂ --> 2NH₃

If we start with 2 moles of N2 and 3 moles of H2, complete BCA table.​

What is the limiting and excess reactants?​

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​	​N2	3H2	​2NH3
​B	​2	​3	​0
​MR	​	​	​
​C = Basis x MR	​	​	​
​A	​	​	​

Limiting and Excess Reagent

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Look at BCA table below for​

N₂ + 3H₂ --> 2NH₃

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Limiting Reactant = H₂ (runs out or is 0 After)

Excess Reactant = N₂ (4 moles are left)​

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​	​N2	​H2	​NH3
​B	​6	​6	​0
C​	​-2	​-6	​+4
A​	​4	​0	​4

Multiple Choice

Which substance is the limiting reactant?

• GaCl₃

• Rb₂S

• RbCl

• Ga₂S₃

Multiple Choice

Which substance is the excess reactant?

• GaCl₃

• Rb₂S

• RbCl

• Ga₂S₃