Effect of Amount Changes on Equilibrium Yields

Part 1: Effect of focus changes on equilibrium yields

THEORY

The solution of Fe(SCN)2+ with that you've been supplied provides the ions Fe3+, SCN- and Fe(SCN)2+ at equilibrium according to the equation :

Fe3+(aq) + SCN-(aq) Fe(SCN)2+(aq)

(pale yellow) (colourless) (blood red)

The intense, blood-red color of the solution is because of the existence of the Fe(SCN)2+(aq) ion. The color of the answer in each test-tube, when seen down the pipe, is a way of measuring the awareness of Fe(SCN)2+(aq) in the pipe. If the volumes are the same in each pipe, then the coloring can be used as a measure of the amount, in mol, of Fe(SCN)2+(aq) in the pipes. By noting how the intensity of the colour changes, it is possible to deduce the effect of each of the testing on the equilibrium. For example, if the color deepens, the amount of Fe(SCN)2+(aq) ions has increased and the amount of the Fe3+(aq) and SCN-(aq) ions must have simultaneously decreased given that they are used up to create more Fe(SCN)2+(aq). The equilibrium would be referred to as having a net forward effect (the position of equilibrium would have 'shifted to the right').

In lab tests A to E the total amount, in mol, of Fe3+(aq) or SCN-(aq) ions present in the answer is initially evolved the following:

In Test A addition of Fe(NO3)3 escalates the amount of Fe3+.

In Test B addition of KSCN increases the amount of SCN-.

In Test C addition of NaF decreases the quantity of Fe3+ because F- ions behave with Fe3+ ions to form FeF63-

In Test D addition of AgNO3 decreases the quantity of SCN- because Ag+ ions react with SCN-ions to create a white precipitate of AgSCN.

In Test E addition of water has no influence on the initial numbers of the two ions, but influences the concentration of most components in the blend.

Refer to Chemistry 2, Chapter 9, for a talk of the consequences of changes in conditions on equilibria.

PROCEDURE and RESULTS

1 Fill up each of six semi-micro test-tubes to 1/3 of its amount with Fe(SCN)2+(aq) solution. Be sure the water in each pipe has the same power of colour when you look down the tube by using a white tile or sheet of paper as a record. If possible, add more solution so the liquid in each tube is the same color. Label the tubes A to F.

2 Using test-tube F for the purposes of assessment, perform each of the tests referred to in the table and record the change occurring in the colour of the perfect solution is when viewed down the tube.

Test-tube Test Shade change

A 1 drop of Fe(NO3)3 added

B 1 drop of KSCN added

C 1 drop of NaF added

D 1 drop of AgNO3 added

E Equal level of water added

F None of them No change

Fe3+(aq) + SCN-(aq) Fe(SCN)2+(aq)

(pale yellow) (colourless) (blood red)

Test Tube

Test

Add

Fe(NO3)3

Add

KSCN

Add

NaF

Add

AgNO3

Add

H2O

Initial effect on. . .

[ Fe3+ ]

INCREASES

[ SCN- ]

[ Fe3+ ]

[ SCN- ]

[ Fe3+ ]

Change in colour

Change in

[Fe(SCN)2+ ]

Consequent change in [Fe3+] and [SCN-]

Comparison of last concentration of the ion with the original concn.

[ Fe3+ ]

GREATER

[ SCN- ]

[ Fe3+ ]

[ SCN- ]

[ Fe3+ ]

Comparison of final amount (mol) of the ion with the original amount

n (Fe3+)

GREATER

n (SCN-)

n (Fe3+)

n (SCN-)

n (Fe3+)

Direction of the shift in equilibrium

Ї

RIGHT

Draw graphs exhibiting the changes in concentration due to the change in the position of equilibrium in each of the assessments A to E (the graph for Test A has been drawn as an example).

Note :

Parts of graphs displaying system at equilibrium should be horizontal lines

Changes in concentration should be roughly in proportion

Concentrations at new position of equilibrium should never go above/below the original values

TEST A

SCN-

Fe(SCN)2+

Fe3+

Concentration

Time

Initial

Equilibrium

Final

Equilibrium

TEST B

Concentration

Time

Initial

Equilibrium

Final

Equilibrium

SCN-

Fe(SCN)2+

Fe3+

TEST C

Concentration

Time

Initial

Equilibrium

Final

Equilibrium

SCN-

Fe(SCN)2+

Fe3+

TEST D

Concentration

Time

Initial

Equilibrium

Final

Equilibrium

SCN-

Fe3+

Fe(SCN)2+

TEST E

Concentration

Time

Initial

Equilibrium

Final

Equilibrium

Fe(SCN)2+

SCN-

Fe3+

Part 2 : Aftereffect of changes in amount on the gaseous equilibrium

THEORY

The syringe contains the gases nitrogen dioxide (NO2) and dinitrogen tetroxide (N2O4) in equilibrium

:

N2O4(g) 2 NO2(g)

(colourless) (dark brown)

N2O4 is a colourless gas, whilst NO2 is a dark brown gas. Subsequently, changes in the focus of NO2 can be checked by watching changes in the power of the color of the gas mixture. In this way, shifts in the positioning of equilibrium can be diagnosed. In this experiment the temp of the concoction is constant therefore the value of the equilibrium constant, K, is unchanged. The effect of the change in amount on gaseous equilibria is referred to in Chemistry 2, Chapter 9.

PROCEDURE

Test 1

Hold a syringe containing an assortment of NO2 gas and N2O4 gas in equilibrium and quickly withdraw the plunger, retaining it constantly in place after getting done so. Please note and track record the change which occurs in the power of the darkish colour the instant the volume is increased and the change in coloring which occurs an instant later.

(You may want to do the test a few times in order to identify both of these changes. )

Observations :

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Test 2

Hold the syringe safely, this time firmly holding the closed end of the syringe. Quickly thrust in the plunger to decrease the volume of gas. Hold the plunger in the new position. Again, take note of and record the change which occurs in the intensity of the darkish colour the moment the volume is reduced and the change that occurs an instant later.

(You may want to do the test a few times in order to recognize both these changes. )

Observations :

QUESTIONS

1. Write an expression for the equilibrium constant, K, for the reaction being looked into.

2. For Test 1 :

a) Account for the initial colour change in conditions of the instantaneous change in attention of NO2.

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

b) Exactly what does the next change in coloring tell us about the concentration of NO2 ?

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

c) Complete the following explanation of the result of the upsurge in level on the equilibrium.

The upsurge in volume initially triggers the concentration of NO2 to. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . and the awareness of N2O4 to. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . The amount small fraction is. . . . . . . . . . . . . . . . . . . . . . . . . . . than the equilibrium constant, K, and the machine is no longer at equilibrium. To get back equilibrium the concentration fraction must. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

The attentiveness of NO2 must. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . while the attention of N2O4 must. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

There is a switch in equilibrium to the. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . leading to the quantity of NO2 to. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . and the quantity of N2O4 to. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

3. For Test 2:

Use Le Chatelier's Concept to explain the change in equilibrium observed when the plunger was pushed in and the quantity of the gas combination decreased.

Part 3: Effect of heat on equilibrium mixtures

THEORY:

According to Le Chatelier's basic principle, a temps change of any equilibrium mixture will elicit a response by the equilibrium mixture, so as to partially oppose the change. The effect on the awareness of the equilibrium components, and hence on the equilibrium constant, is determined by whether the response is exothermic or endothermic, and on the route of the temperature change.

Refer to Heinemann Chemistry Two, Section 9, for further discussion of the result of heat change on chemical equilibrium.

PROCEDURE AND RESULTS

A. N2O4 (g) 2NO2 (g) ; endothermic. (Take note of : N2O4 is colourless and NO2 is darkish)

Carefully place one of the stoppered test-tubes including an N2O4 / NO2 gas concoction in a beaker of warm water for about about a minute, keeping the stopper tightly in place. Place the other tube in a beaker of ice water.

Remove the tubes from the hot water and ice-water and immediately compare the intensities of the dark brown coloring in the tubes. Track record your observations.

Hot drinking water. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Cold drinking water. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

B. Fe3+(aq) + SCN- (aq) Fe(SCN)2+ (aq) ; exothermic. (Red coloring is because of Fe(SCN)2+)

Half-fill two semi-micro test-tubes with Fe(SCN)2+ solution.

Place one test-tube in a beaker of snow normal water. Place the other test-tube into a beaker of very hot water.

Compare the colour of the mixtures in the two test-tubes. Track record your observations.

Hot water. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Cold water. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

C. H3PO4 (aq) H2PO4- (aq) + H+ (aq) ; exothermic (Methyl violet signal)

(Green - Blue - Violet as pH boosts)

Pour 1M orthophosphoric acid (H3PO4), into each of two semi-micro test-tubes, to a depth of about 3 cm. Add one drop of methyl violet sign to each test-tube.

Place one test-tube in a beaker of snow drinking water. Place the other test-tube into a beaker of scorching water. Record the colour of the indicator in each one of the two test-tubes.

Note the acidity of each solution. Methyl violet signal is yellowish in solutions with a high attentiveness of H+ (aq) (low pH) and its own colour changes through renewable to blue and to violet as the H+ (aq) attentiveness reduces (ie with increasing pH).

QUESTIONS

In Part A, the brown coloring in the test-tubes supplied is due to the presence of nitrogen dioxide (NO2) gas.

How will the concentration of nitrogen dioxide in the equilibrium concoction change as the temps is increased?

What does indeed your experiment indicate happens to the value of the equilibrium constant, K, because of this reaction as the temperatures rises? Explain.

Describe (using Le Chatelier's process) the way the equilibrium position has shifted.

In Part B, the red color is caused by the ion Fe(SCN)2+.

How does the amount of Fe(SCN)2+ ions in the equilibrium combination change as the temperatures is increased?

What will this indicate about the value of the equilibrium constant, K, for this response as the heat raises? Explain.

Describe (using Le Chatelier's rule) the way the equilibrium position has shifted. .

Account for your observations in Part C of the test (H3PO4 (aq))

Effect of Awareness Changes on Equilibrium Yields

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