Aha! Chemistry with Prof Bob
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  • LEARNING MODULES
    • Chapter 02 Stuff, matter: What is it? >
      • 0200 Stuff, matter: A theory of atoms
      • 0201 Atoms: The building blocks of all stuff
      • 0202 People classifying stuffs. Why?
    • Chapter 05 Chemical reactions and chemical equations >
      • 0500 Chemical reactions and chemical equations. Overview
      • 0501 Chemical amount and its unit of measurement, mole
      • 0502 The Avogadro constant: How many is that?
      • 0503 The Avogadro constant: Why is it that number?
      • 0504 Chemical formulas: What can they tell us??
      • 0505 Chemical equations: What can they tell us?
      • 0506 Limiting reactants: How much reaction can happen?
      • 0507 Balanced chemical equations: What are they?
      • 0508 Chemical reactions as competitions
    • Chapter 09 Aqueous solutions >
      • 0901 What is a solution? And what is not?
      • 0902 Miscibility of liquids in each other
      • 0903 Like dissolves like? Shades of grey
      • 0905 Dissolution of ionic salts in water: A competition
      • 0906 Can we predict solubilities of salts?
      • 0907 Solution concentration
      • 0908 Chemical species, speciation in aqueous solution
      • 0909 Solutes: Electrolytes or non-electrolytes?
      • 0910 Electrolytes - strong or weak?
      • 0911 Concentrated, dilute, strong, weak
      • 0912 Species concentration vs. solution concentration
      • 0913 Weak electrolytes: Getting quantitative
    • Chapter 11: Dynamic chemical equilibrium >
      • 1100 Dynamic chemical equilibrium: Overview
      • 1101 Visualising dynamic chemical equilibrium
      • 1102 The jargon of chemical equilibrium
      • 1103 Equilibrium constants: The law of equilibrium
      • 1104 The law of equilibrium: an analogy
    • Chapter 22 Evidence from spectroscopy >
      • 2200 Spectroscopy: Overview and preview
      • 2201 Quantisation of forms of energy
      • 2202 Light: Wave-particle "duality"
      • 2203 Ultraviolet-visible spectroscopy
      • 2204 Beer’s law: How much light is transmitted?
    • ENVIRONMENTAL CHEMISTRY >
      • EARTH'S ATMOSPHERE >
        • Chapter 27 The greenhouse effect, climate change >
          • 2700 The greenhouse effect: overview
          • 2701 Is Earth in energy balance?
          • 2702 CO2 in the atmosphere before 1800
          • 2703 So little CO2! Pffft?
          • 2704 Does CO2 affect Earth's energy balance?
          • 2705 The "greenhouse effect"
          • 2706 Why does CO2 absorb radiation from Earth?
          • 2707 The "enhanced greenhouse effect"
          • 2708 Why doesn't CO2 absorb the radiation from the sun?
          • 2709 Why are N2 and O2 not greenhouse gases?
          • 2710 Doesn't water vapour absorb all the IR?
          • 2711 Carbon dioxide from our cars
          • 2712 The source of energy from combustion
          • 2713 Comparing fuels as energy sources
          • 2714 Methane: How does it compare as a GHG?
          • 2715 Different sorts of pollution of the atmosphere
          • 2716 "Acidification" of seawater
      • FUELS
      • EARTH'S OCEANS AND WATERWAYS
  • TEACHERS' CORNER
    • TC01 Language and meaning in chemistry >
      • TC0101 The jargon we use
    • TC02 REPRESENTATION IN CHEMISTRY
    • TC03 MODELLING IN CHEMISTRY
    • TC04 KNOWING AND LEARNING
    • TC05 Communicating chemistry >
      • TC0501 Overview, preview
    • TC06 COMPLEXITY of LEARNING CHEMISTRY
    • TC07 PEDAGOGOICAL CONTENT KNOWLEDGE, PCK >
      • TC0701 Amnesia of the chemistry teaching professioN
    • MODULE-SPECIFIC PCK >
      • Chapter PCK11 Dynamic chemical equilibrium >
        • PCK1101 Visusalizing dynamic chemical equilibrium
        • PCK1103 Equilibrium constants: The law of equilibrium
      • Chapter PCK22 Evidence from spectroscopy >
        • PCK2204 Beer's law
  • NAVIGATION
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    • Index, alphabetical
Module 0506

​

Limiting reactants: How much reaction can happen?

 What limits how much reaction can happen?

The amount of one of the reactants

​Which one? Why?

Why is the balanced equation important?

Preamble and context


​Do reactions go until all of the reactants are 'used up'? Almost never.

Even when the condition of equilibrium is so one-sided in the direction of the products, when one of the reactants has completely reacted, there will still be some of the other(s) remaining unreacted.

​What limits how much reaction can happen (when there is no more of one reactant left, so that no further reaction is possible)?

Learning chemistry related to these ideas is limited without sufficient knowledge of the content of at least module 0501 Chemical amount and its unit of measurement, the mole;  Module 0505 Chemical equations: What can they tell us? and Module 0507 Balanced chemical reactions; What are they?

Qualifiying note: Closed systems


The discussion in this module about the amount of a reactant that limits further reaction applies to reaction mixtures that are called "closed systems" - that is, happening in a vessel to which none of the reactants or products are added nor removed. This excludes naturally occurring chemical reactions, such as photosynthesis, in which the reactants are continuously being replaced, and the products continuously removed.


​
Aussie and Prof Bob talk it through .....
Aussie has Aha! moments about which reactant limits the amount of reaction that can happen in a reaction mixture.
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​KEY IDEAS - Limiting reactants: How much can happen?
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Just when it seemed that the reaction was going gangbusters, the limiting reactant ran out.

Limiting reactant: the one that 'runs out' first

The ability to decide which reactant in a reaction mixture limits the amount of reaction that can happen is dependent on knowing the balanced chemical equation that represents the chemical change.

​The amount (in moles) of substances that can react with each other is limited by the amount of that one which is used up first. This is called the limiting reactant.

More reaction can happen if we add more of the limiting reactant. But no more reaction can result from addition of the other reactant – we would just have more of it left unreacted (we say “in excess”).

Stoichiometric calculations (How much of this reacts? How much of that is formed) must be based on the amount (in moles) of the limiting reactant present in the reaction mixture, taking into account the ratio of amounts that react with each other as indicated by the balanced chemical equation for the reaction.

The trick is to understand, given the balanced chemical equation, which reactant will 'run out' first.


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SELF CHECK: Some thinking tasks
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I understand about limiting reactants! I think ......... Let me check
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The reaction takes place in a closed vessel.
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ANSWERS
​
1    (a) E (10)     
      (b) B (cheese)
      (c) D (20)

​2     D 
3    (a) 2.5 mol     
      (b) 1.60 mol     
      (c) 1,80 mol
      (d) 0.80 mol; O2(g)
​      (e) 1,60 mol; C8H18(g)
Finding your way around .....

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LEARNING CHEMISTRY FOR UNDERSTANDING

Email: [email protected]


​© The content on any page in this website (video, text, original images, and self-check) may be used without charge for non-commercial educational purposes, provided that acknowledgement is given to the Aha! Learning Chemistry with Prof Bob website, with specification of the URL: https://www.ahachemistry.com/​
  • HOME
    • TALK WITH PROF BOB?
  • LEARNING MODULES
    • Chapter 02 Stuff, matter: What is it? >
      • 0200 Stuff, matter: A theory of atoms
      • 0201 Atoms: The building blocks of all stuff
      • 0202 People classifying stuffs. Why?
    • Chapter 05 Chemical reactions and chemical equations >
      • 0500 Chemical reactions and chemical equations. Overview
      • 0501 Chemical amount and its unit of measurement, mole
      • 0502 The Avogadro constant: How many is that?
      • 0503 The Avogadro constant: Why is it that number?
      • 0504 Chemical formulas: What can they tell us??
      • 0505 Chemical equations: What can they tell us?
      • 0506 Limiting reactants: How much reaction can happen?
      • 0507 Balanced chemical equations: What are they?
      • 0508 Chemical reactions as competitions
    • Chapter 09 Aqueous solutions >
      • 0901 What is a solution? And what is not?
      • 0902 Miscibility of liquids in each other
      • 0903 Like dissolves like? Shades of grey
      • 0905 Dissolution of ionic salts in water: A competition
      • 0906 Can we predict solubilities of salts?
      • 0907 Solution concentration
      • 0908 Chemical species, speciation in aqueous solution
      • 0909 Solutes: Electrolytes or non-electrolytes?
      • 0910 Electrolytes - strong or weak?
      • 0911 Concentrated, dilute, strong, weak
      • 0912 Species concentration vs. solution concentration
      • 0913 Weak electrolytes: Getting quantitative
    • Chapter 11: Dynamic chemical equilibrium >
      • 1100 Dynamic chemical equilibrium: Overview
      • 1101 Visualising dynamic chemical equilibrium
      • 1102 The jargon of chemical equilibrium
      • 1103 Equilibrium constants: The law of equilibrium
      • 1104 The law of equilibrium: an analogy
    • Chapter 22 Evidence from spectroscopy >
      • 2200 Spectroscopy: Overview and preview
      • 2201 Quantisation of forms of energy
      • 2202 Light: Wave-particle "duality"
      • 2203 Ultraviolet-visible spectroscopy
      • 2204 Beer’s law: How much light is transmitted?
    • ENVIRONMENTAL CHEMISTRY >
      • EARTH'S ATMOSPHERE >
        • Chapter 27 The greenhouse effect, climate change >
          • 2700 The greenhouse effect: overview
          • 2701 Is Earth in energy balance?
          • 2702 CO2 in the atmosphere before 1800
          • 2703 So little CO2! Pffft?
          • 2704 Does CO2 affect Earth's energy balance?
          • 2705 The "greenhouse effect"
          • 2706 Why does CO2 absorb radiation from Earth?
          • 2707 The "enhanced greenhouse effect"
          • 2708 Why doesn't CO2 absorb the radiation from the sun?
          • 2709 Why are N2 and O2 not greenhouse gases?
          • 2710 Doesn't water vapour absorb all the IR?
          • 2711 Carbon dioxide from our cars
          • 2712 The source of energy from combustion
          • 2713 Comparing fuels as energy sources
          • 2714 Methane: How does it compare as a GHG?
          • 2715 Different sorts of pollution of the atmosphere
          • 2716 "Acidification" of seawater
      • FUELS
      • EARTH'S OCEANS AND WATERWAYS
  • TEACHERS' CORNER
    • TC01 Language and meaning in chemistry >
      • TC0101 The jargon we use
    • TC02 REPRESENTATION IN CHEMISTRY
    • TC03 MODELLING IN CHEMISTRY
    • TC04 KNOWING AND LEARNING
    • TC05 Communicating chemistry >
      • TC0501 Overview, preview
    • TC06 COMPLEXITY of LEARNING CHEMISTRY
    • TC07 PEDAGOGOICAL CONTENT KNOWLEDGE, PCK >
      • TC0701 Amnesia of the chemistry teaching professioN
    • MODULE-SPECIFIC PCK >
      • Chapter PCK11 Dynamic chemical equilibrium >
        • PCK1101 Visusalizing dynamic chemical equilibrium
        • PCK1103 Equilibrium constants: The law of equilibrium
      • Chapter PCK22 Evidence from spectroscopy >
        • PCK2204 Beer's law
  • NAVIGATION
    • Table of contents
    • Index, alphabetical