Introduction to Equilibria

Module 5: Equilibrium Intro

12 Chem

​Syllabus dot points

• ​5.1 a/b:

• conduct practical investigations to analyse the reversibility of chemical reactions, for example:

– cobalt(II) chloride hydrated and dehydrated

– iron(III) nitrate and potassium thiocyanate

– burning magnesium

– burning steel wool

model static and dynamic equilibrium and analyse the differences between open and closed systems

​What we will learn...

• ​Overview of the 1st IQ

• ​Open and closed systems

• Reversible and irreversible reactions

• ​Dynamic Equilibrium

• ​Static equilibrium

​First IQ of Module 5

• ​knowledge from Year 11

  • ​enthalpy and entropy

  • ​systems and surroundings

  • ​combustion rxns

  • ​collision theory

​Open and Closed Systems

• ​Open systems exchange energy AND matter with surroundings

• ​Closed systems only exchange energy

• ​System = the reaction

• ​Surroundings = everything else

​Reversible vs. Irreversible Reactions

• ​irreversible = the products do not react again to reform the reactants

• ​reversible = products react again in the reverse to reform reactants

  • ​particles need to collide with enough energy

• ​now we think about equilibrium with reversible reactions

​Equilibrium and Collision Theory

• ​the the rxn has appeared to stop (i.e. concentrations of reactants and products stay constant), at an atomic scale the rxn is still occurring

  • ​The forward and reverse rxn are happening at the same rate

  • ​this is dynamic equilibrium

​or can use conc vs time 

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​As when no further changes to concentration occur, equilibrium is established 

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​Dynamic Equilibrium

• ​in a closed system

• ​involves an irreversible reaction

• ​rate of forward and reverse reactions is the same

• ​concentrations of products and reactants are constant

• ​macroscopic properties are constant, microscopic still happening

• ​ratios of reactants to products is different in differing equilibrium systems

​Static Equilibrium

• ​not often used in chemistry

• ​but, it is when the forward and reverse reactions are zero

  • ​for example, graphite into diamond

• ​we do have non-equilibrium systems

  • ​irreversible and do not reach equilibrium

  • ​combustion

  • ​photosynthesis

Multiple Choice

This symbol indicates that a reaction is ____________

• reversible

• irreversible

Multiple Choice

When the rate of the forward reaction is equal to the rate of backward reaction, the system is said to be in

• Chemical Equilibrium

• Chemical Balance

• Chemical Constant

• Chemical Reaction

Multiple Choice

Which of the following statements about open systems is correct? 

• An open system can exchange matter and energy with the surroundings 

• An open system can exchange nothing with the surroundings 

• An open system can exchange only matter with the surroundings

• An open system can exchange only energy with the surroundings

Multiple Choice

At what time is equilibrium reached?

• 0 s

• 2 s

• 4 s

• 10s

​What we will look at next...

• ​calculating equilibrium constant

• ​effects of temperature on equilibrium/changes to equilibrium