# 3.2 Chemical equilibrium

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## Chemical equilibrium

Having looked at factors that affect the rate of a reaction, we now need to ask some important questions. Does a reaction always proceed in the same direction or can it be reversible? In other words, is it always true that a reaction proceeds from reactants to products , or is it possible that sometimes, the reaction will reverse and the products will be changed back into the reactants ? And does a reaction always run its full course so that all the reactants are used up, or can a reaction reach a point where reactants are still present, but there does not seem to be any further change taking place in the reaction? The following demonstration might help to explain this.

## Demonstration : liquid-vapour phase equilibrium

Apparatus and materials:

2 beakers; water; bell jar

Method:

1. Half fill two beakers with water and mark the level of the water in each case.
2. Cover one of the beakers with a bell jar.
3. Leave the beakers and, over the course of a day or two, observe how the water level in the two beakers changes. What do you notice? Note: You could speed up this demonstration by placing the two beakers over a bunsen burner to heat the water. In this case, it may be easier to cover the second beaker with a glass cover.

Observations:

You should notice that in the beaker that is uncovered, the water level drops quickly because of evaporation. In the beaker that is covered, there is an initial drop in the water level, but after a while evaporation appears to stop and the water level in this beaker is higher than that in the one that is open. Note that the diagram below shows the situation ate time=0.

Discussion:

In the first beaker, liquid water becomes water vapour as a result of evaporation and the water level drops. In the second beaker, evaporation also takes place. However, in this case, the vapour comes into contact with the surface of the bell jar and it cools and condenses to form liquid water again. This water is returned to the beaker. Once condensation has begun, the rate at which water is lost from the beaker will start to decrease. At some point, the rate of evaporation will be equal to the rate of condensation above the beaker, and there will be no change in the water level in the beaker. This can be represented as follows:

$liquid⇌vapour$

In this example, the reaction (in this case, a change in the phase of water) can proceed in either direction. In one direction there is a change in phase from liquid to vapour. But the reverse can also take place, when vapour condenses to form water again.

In a closed system it is possible for reactions to be reversible, such as in the demonstration above. In a closed system, it is also possible for a chemical reaction to reach equilibrium . We will discuss these concepts in more detail.

## Open and closed systems

An open system is one in which matter or energy can flow into or out of the system. In the liquid-vapour demonstration we used, the first beaker was an example of an open system because the beaker could be heated or cooled (a change in energy ), and water vapour (the matter ) could evaporate from the beaker.

Do polymers form restrictedly only if compound is saturated, only?
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is when The Only Force acting On an Object is Gravitational Force
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on What?
the organic molecule section
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IUPAC NAMING WHICH FUNCTIONAL GROUP YOU CANNOT NAME?SO I COULD HELP YOU
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you should also look at structural isomers. Its crucial that they might add that one. also try and write down the structural formula of all the given compounds on the table
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a functional group depends on how many bonds there are between carbon atoms, if there are single bonds all the way it's an alkane, if there is a presence of at least one double bond it's a Alkene and if there's at least one triple bond it's an alkyne.
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work
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is Power Not Work work is Measured In Joules it has Energy
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is an electrochemical cell that derives electrical energy from spontaneous redox reactions taking place within the cell.
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suffix Ane in the IUPAC NAMING
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Alkanes are Saturated Meaning they don't have Multiple Bonds between Carbon Atoms and When you are Naming THEM THEY MUST END WITH (-ANE ) GET ME?
What are hydrocarbons
are organic Compounds with only Carbon and Hydrogen Atoms
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definition of chain parent
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when butane burns in an excess of oxygen ,the products are
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CO2 and H2O
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Carbon dioxide and Water...
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Hydrocarbon is a compostion of mainy carbon and hydrogen
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hydrocarbon compound made up of carbon and hydrogen only
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25 element of physics
an object will remain at rest or move at a constant velocity unless acted upon a net force
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law of inertia
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an object resisting the change in velocity.
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newton first law of motion
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An object will remain at rest, unless an unbalanced force acts on it.
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or uniform motion
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What is a molecule
a molecule is a simplest structure unite of an elements
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