Topic G: Chemical Equilibrium Flashcards

1
Q

What is dynamic equilibrium

A

When the rates of the forward and reverse reaction are equal. The reaction has not stopped, just that forward and backward reactions are occurring at the same rate

The concentration of all the reactants and products remain constant if the temperature is kept constant

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2
Q

How is it shown on a graph when dynamic equilibrium is reached

A

For concentration-time graph, it is when the concentration of the reactants becomes constant

For rate-time graph, it is when the rate of both forward and backward reactions become equal

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3
Q

What is homogenous chemical equilibrium

A

Systems where the reactants and products are in the same physical states

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4
Q

What is heterogenous equilibrium

A

It occurs when one or more of the reactants or products is in a different phase to the other reactants or products

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5
Q

Why do solids not appear in the formula for equilibrium constant

A

Solids do not have concentrations

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6
Q

Why does the concentration of pure solids or liquids not appear in the expression for equilibrium constant

A

The concentration of a pure solid or a pure liquid is similar to its density, which remains almost constant at any temperature

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7
Q

What do the different values of K tell us about a reaction

A

If K &laquo_space;1: Reaction has hardly proceeded
If K < 1: Equilibrium lies towards reactants and the mixture contains mainly the reactants
If K = 1: Both reactants and products at equilibrium
If K > 1: Equilibrium lies towards products and the mixture contains mainly the products
If K&raquo_space; 1: Reaction goes almost to completion

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8
Q

What is the value of K dependent and not dependent on

A

The value of K is only temperature dependent

It is not dependent by:
- Change in concentration of reactants or products
- Change in the pressure of the system
- The presence of a catalyst

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9
Q

What is Le Chatelier’s Principal

A

If a change is made to the conditions of a system at dynamic equilibrium, then the position of equilibrium will shift to counteract the change and establish a new equilibrium

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10
Q

What happens if some reactants is added to a reaction at equilibrium

A

The forward reaction works to remove excess reactant added and POE shifts from left to right
Reactants react to produce more products
At the new equilibrium, there will be more products but less of the other reactant

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11
Q

What happens if some reactants is removed from a reaction at equilibrium

A

The reverse reaction works to replace the removed reactant and the POE shifts from right to left
Products react to produce more reactants
At the new equilibrium, there is less products but more of the other reactant

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12
Q

What happens if the pressure of a system in equilibrium is increased

A

This causes the POE to move in the direction that results in a decrease in the total number of moles of gaseous particles

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13
Q

What happens if the pressure of a system in equilibrium is decreased

A

This causes the POE to move in the direction that results in an increase in the total number of moles of gaseous particles

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14
Q

What happens if there is an increase in reaction temperature to a reaction at equilibrium

A

The POE shifts to favour the endothermic reaction to remove some heat energy
K changes

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15
Q

What happens if there is a decrease in reaction temperature to a reaction at equilibrium

A

The POE shifts to favour the exothermic reaction to produce some heat energy
K changes

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16
Q

Does a catalyst change the POE of a reaction, why

A

No, because catalysts increase the rate constants of both the forward and backward reactions by the same extent

17
Q

What is the reaction quotient (Q)

A

The expression is similar to the one used to calculate equilibrium constant K, but Q can be calculated for any set of conditions, not just for equilibrium

18
Q

How can reaction quotient (Q) be used to determine a reaction direction

A

Q can be used to determine which direction a reaction will shift to reach equilibrium
If K > Q, the reaction will proceed forward, converting reactants into products
If K < Q, the reaction will proceed backwards in the reverse direction, converting products into reactants
If Q = K, the system is at equilibrium

19
Q
A