Embedded Files
objectives
objectives
Understandings
- A state of equilibrium is reached in a closed system when the rates of the forward and reverse reactions are equal.
- The equilibrium law describes how the equilibrium constant (Kc) can be determined for a particular chemical reaction.
- The magnitude of the equilibrium constant indicates the extent of a reaction at equilibrium and is temperature dependent.
- The reaction quotient (Q) measures the relative amount of products and reactants present during a reaction at a particular point in time. Q is the equilibrium expression with non-equilibrium concentrations. The position of the equilibrium changes with changes in concentration, pressure, and temperature.
- A catalyst has no effect on the position of equilibrium or the equilibrium constant.
Applications and skills:
- The characteristics of chemical and physical systems in a state of equilibrium.
- Deduction of the equilibrium constant expression (Kc) from an equation for a homogeneous reaction.
- Determination of the relationship between different equilibrium constants (Kc) for the same reaction at the same temperature.
- Application of Le Châtelier’s principle to predict the qualitative effects of changes of temperature, pressure and concentration on the position of equilibrium and on the value of the equilibrium constant.
Guidance:
- Physical and chemical systems should be covered.
- Relationship between Kc values for reactions that are multiples or inverses of one another should be covered.
- Specific details of any industrial process are not required.
Open and Closed Systems
Open and Closed Systems
As Products and Reactants are being made at a constant rate it is a fair comparison to explain that Equilibrium reactions often appear in balance
This explanation can mean that as the products and reactants amounts are constantly produced then their associated amounts appear not to change
This means that if Matter or Energy can be changed in the reaction then this would cause the reaction to be imbalanced. Equilibrium reactions will always try to oppose these changes in order to make the reaction balanced meaning that if it is possible to adjust matter or energy in a chemical reaction then this will adjust the reaction itself.
When chemical reactions occur they occur in an area called a Reaction System - there are three types of system we need to learn in this qualification.
Types of Reaction System
Types of Reaction System
A Thermodynamic System is an important aspect of any chemical reaction as it allows us to clearly define how matter and energy is exchanged within a particular part of the universe. This sounds like quite an abstract concept but the area we define as a reaction system is usually very small and everything else would therefore be defined as the surroundings.
A system is therefore a part of the universe being studied
The surroundings are the rest of the universe that interact with the system
All Systems are composed of an area where the reaction is taking place and the Boundary which is th edge of the reaction area
Open System
Open System
In an open system, mass and energy both may be transferred between the system and surroundings.
Closed System
Closed System
In a closed system Mass cannot be transferred across the boundary however transfer of energy (work and or heat) takes place
Isolated Systems
Isolated Systems
An isolated system cannot exchange both energy and mass with its surroundings
Comparing different Reaction Systems
Comparing different Reaction Systems
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