Karteikarten
Equilibrium
Karten in diesem Stapel (77)
- 1Explain what equilibrium state is.In a chemical reaction when a reaction takes place at the same rate as its reverse reaction so no net change is observed.
- 2Explain what happens when Bromine (Bré) is placed in a sealed container at room temperature.Bromine is a volatile liquid with a bp close to room temp. Because of this, many particles (Br2 molecules) will have sufficient energy to leave the liquid state and from vapour in the process=evaporation.
Since the container is sealed, the vapour of bromine cannot escape and so its concentration will increase. Some of the vapour molecules will collide with the surface of the liquid, lose energy, and become liquid again=condensation. - 3Explain the trend in condensation with concentration of vapour in terms of equilibriumRate of condensation=rate of evaporation
The rate of condensation increases with the increase in concentration of vapour, as more vapour particles collide with the surface of the liquid. Eventually, the rate of condensation is EQUAL to the rate of evaporation, and at this point there will be no net change in the amounts of liquid and gas present. The system has reached equilibrium (but can only occur in a closed system where the gas cannot escape as vapour but may condense back to liquid) - 4Explain this graphThe rates of evaporation and condensation as liquid-vapour equilibrium are established in a closed system. The rate of evaporation is constant, while the rate of condensation increases with increasing concentration of vapour. Equilibrium is established when the two rates are equal.
- 5What is dynamic in terms of equilibrium?The reaction has not stopped but both forward and backward reactions are still occuring at the same rate
- 6What is equilibrium mixture?;
- 7Why do many reactions go to completion? Give an example of a reaction.The products are much more energetically favourable than the reactants and the activation energy is low enough for a rapid reaction at an ambient temperature. This means the reaction continues until one of the reactants is completely used up. When this happens the reaction stops.
NaOH + HCl --> NaCl + H2O - 8Reversible reactions are reactions in which...There is always a measurable amount of reactants as well as products
- 9In what conditions can the chemical equilibrium be established?If the reaction is in a closed system at constant temperature and no gases can escape.
- 10In equilibrium, why are only reactants initially present and the rate of the forward reaction is at its fastest?because the reactants are at their highest concentration
- 11Info cardInitially only reactants are present and the rate of the forward reaction is at its fastest since the reactants are at their highest concentration. The forward reaction slows down as the reactant concentration goes down. As products form, the rate of the backward reaction increases. Eventually, the point is reached when the rate of the forward reaction equals the rate of the backward reaction. There is no further observable change. The macroscopic properties of a system, such as colour, density, pH etc. remain constant. The reaction has reached chemical equilibrium. This is dynamic equilibrium
- 12At equilibrium, the rate of the forward reaction=.....the rate of the backward reaction
- 13At equilibrium, what remains constant?The concentrations of te reactants and the products
- 14At equilibrium, there is no change in...the macroscopic properties such as colour and density
- 15At equilibrium, the equilibrium can be approached from....either the forward or the reverse direction
- 16The equilibrium is dynamic. The forward and reverse reactions continue but...there is no overall change in the concentration of reactant and products occur
- 17Info cardAny changes to the reaction conditions, such as temperature, pressure, concentration of reactants or products can affect the equilibrium, demonstrating its dynamic nature.
- 18Explain in detail about what would happen if bromine liquid is placed in a sealed flask, in terms of equilibriumSome liquid bromine molecules have sufficient energy to escape into the air above the liquid. Initially the rate of evaporation is at a maximum. As the concentration of the bromine vapour increases some molecules may convert back to liquid bromine. The rate of condensation is slow at first. The rate of vaporisation decreases and the rate of condensation increases until the equilibrium is established and both forward and backward occur at the same rate. The concentration of bromine vapour remains constant.
- 19If concentrations are high and little reactants are left then equilibrium is said to be...right
- 20If products concentrations are low and reactants have high concentration then the equilibrium is said to be...left
- 21The concentration of the species at equilibrium will reflect ...how readily they react on collision
- 22The lower the concentration of a species at equilibrium, the ______________ it reacts.more easily
- 23The rate at which a reaction occurs depends on.....The concentration of the species involved
- 24Forward rate=Kf[A][B]
- 25Backward rate=Kr[C][D]
- 26Why does: Kf[A][B]=Kr[C][D]because at equilibrium, rates are equal
- 27info cardKf [C][D]
--- = ----------------
Kr [A][B] - 28What is equilibrium constant?As Kr and Kf are constants, at a given temperature, their ratio is constant and is known as the equilibrium constant, Kc
- 29If the concentration of the species involved are all 1.0 mol dm-3, the Kc =Value of 1
- 30If Kc is greater than one, then the concentration of products are ....greater than those of the reactants and the equilibrium is said to lie on the right hand side
- 31If Kc is very large, the reaction can be regarded as...going to completion
- 32If Kc is less than one; then the equilibrium...lies to the left
- 33If Kc is very small, the reaction may be considered...not to occur
- 34What does the law of chemical equilibrium state?That at a given temperature the ratio of the concentration of products (raised to their power of their coefficients) to the concentration of the reactants (raised to the power of their coefficients) is a constant
- 35Info cardThe concentrations of certain substances remain constant (all solid and pure liquids) so are not included in the equilibrium constant and are omitted from the express. In dilute aqueous solution the concentration of water is taken as constant and is omitted, whereas when water is not in aqueous solution or is in the gas phase it must be included in the equilibrium expression.
- 36info cardIf there are multiple steps in a reaction each with its own equilibrium constant, then the equilibrium constants are multiplied to give the overall value of Kc
- 37What does Le Chatelier's principle state?If a change is made to the conditions of a chemical equilibrium, then the position of equilibrium will readjust so as to minimise the change made.
- 38What does changes in concentration and pressure affect? What do they not affect? Explainthe position of equilibrium and the amounts of various species present. They have no effect on the value of the equilibrium constant Kc. This is because the values of the rate constant Kf and Kr do not change. A change of temperature however, does affect the rate constants, so the value of Kc changes and as well ad the positon.
- 39What does the presence of a catalyst do? Therefore...Reduces the activation energy of both the forward and backward reaction by the same amount. Therefore the reaction reaches equilibrium faster. There is no change to the equilibrium constant or to the position of the equilibrium.
- 40A + B <-----> C + D If the concentration of C increases then...the rate of the reverse reaction increases so the reaction rates are no longer equal
- 41info cardA + B <-----> C + D
If the concentration of C increases then the rate of the reverse reaction increases so the reaction rates are no longer equal. In order to restore equilibrium, the amount of the A + B must increase and the C + D decrease- the equilibrium shifts to the left. The amount of C decreases to below its new higher level, but is still higher than the original level - 42A + B <-----> C + D If the concentration of C increases then the rate of the reverse reaction increases so the reaction rates are no longer equal. What needs to be done in order to restore equilibrium?the amount of the A + B must increase and the C + D decrease- the equilibrium shifts to the left. The amount of C decreases to below its new higher level, but is still higher than the original level
- 43What will equilibria involving gases be affected by?Change in pressure- if the reaction involves a change in th number of molecules
- 44Info cardsince equilibria involving gases will be affected by a change in pressure- if the reaction involves a change in th number of molecules,
if the reaction:
A(g) + B(g) <-----> C(g) + 2D(g)
Is subjected to an increase in pressure,
the system responds to decrease this pressure by favouring the side with the smaller number of gas molecules - 45What else increases when pressure is increased? (On the topic of position of equilibrium)The rate at which gases react
- 46Info Card(On the topic of position of equilibrium)
If pressure is increased, the rate at which gases react will also increase. The more moles of gas involved on the side of the equilibrium, the more the increase in pressure will affect the rate.
This shifts the position of the equilibrium, but the equilibrium constant remains the same - 47(On the topic of position of equilibrium) what increases with the increase in temperature?The rate of the forward and reverse (but not by the same amount)
- 48Info cardIf the temperature increases, then the rate of the forward and reverse reaction will increases but not by the same amount. The reaction will speed up more in the endothermic direction. This change absorbs heat energy and causes the temperature to fall to below its new higher value.
- 49The higher the activation energy, the greater the ...the effect on reaction rate
- 50info cardthe higher the activation energy, the greater the effect on reaction rate so that an increase in temperature will speed up the reaction in the endothermic direction (which must have a greater activation energy) more than the exothermic energy. This will increase the rate constant of the endothermic reaction more than for the exothermic reaction. The value of the equilibrium constant, Kc, changes.
- 51Info card[Temperature dependence of Kc: From the Arrhenius equation k=Ae]
we know that the rate constant increase with increasing temperature. As the activation energy of the forward and backward reactions are different, their rate constants Kf and Kr are differently affected by temperature. So the ratio Kf/Kr, the equilibrium constant Kc, is temperature dependent.
The endothermic reaction has a higher activation energy than the exothermic direction. There is therefore a greater effect on increasing the rate constant of the endothermic reaction than the exothermic rate constant. This changes Kc. - 52What is a catalyst?A substance that speeds up the rate of a chemical reaction but is not used up in the reaction
- 53What does a catalyst do in terms of equilibrium?Speeds up the rate at which equilibrium is reached
- 54How does a catalyst work? [on topic of equilibrium]By providing an alternate pathway with a lower activation energy. However, this alternative pathway will have a lower activation energy for both the forward and the reverse reaction. The result is that the rates of both forward and reverse reactions will be increased and equilibrium will be reached more quickly.
- 55(On the topic of equilibrium) What does a catalyst not affect? Why/How?The position of equilibrium or the value of the equilibrium constant.
Adding a catalyst increases the values of the forward and backward rate constant by the same factor so the ratio of their values, the equilibrium constant, is not affected. - 56What is a homogenous equilibrium?One in which all the reactants and products are in the same phase.
- 57Info card(On the topic of homogenous equilibrium and equilibrium law)
The concentrations, when substituted into the equilibrium constant formula, will only equal the equilibrium constant if the reaction is in fact in equilibrium.
For other situations the value produced by treating the concentrations in the same way will indicate which way the reaction needs to shift in order to reach equilibrium. - 58(On the topic of equilibrium) What is the reaction quotient Q? What does this help us to determine?The ratio of the concentration of product to reactants when not in equilibrium
It helps us to determine the progress of the reaction and the direction that is favoured to establish equilibrium. - 59Q>Kc means?The concentration of the products is greater than at equilibrium and the reverse reaction is favoured until equilibrium is reached
- 60QThe concentration of the products is greater than at equilibrium and the forward reaction is favoured until equilibrium is reached
- 61Q=Kc means?The system is a equilibrium and the forward and reverse reactions occur at equal rates
- 62Name 5 factors which affect equilibria-concentration
-temperature
-pressure
-catalysts
-surface area - 63what is the effect of concentration on equilibrium position?Increase the reactant, and the product increase and vice versa
increase product, then reactant increases and vice versa - 64Explain the statement, "equilibrium is achieved in a closed system"A closed system has no exchange of matter with the surroundings, so equilibrium is achieved where both reactants and products can react and recombine with each other
- 65Explain the statement "the concentrations of reactants and products remain constant at equilibrium"They are being produced and destroyed at an equal rate
- 66Explain the statement "At equilibrium there is no change in macroscopic properties"macroscopic properties are observable properties for example colour or density. These do not change as they depends on the concentration of the components of the mixture
- 67Explain the statement "equilibrium can be reached from either direction"The same equilibrium will results under the same conditions, no matter whether the reaction is started with all reactants, all products or, a mixture of both
- 68info cardJust because at equilibrium the concentration of the products and reactants are constants does not mean they are equal
- 69what is equilibrium position?The proportion of reactant and product in the equilibrium mixture
- 70In reactions where the mixture contains predominantly products, they are said to "lie to the _____"right
- 71In reactions where the mixture contains predominantly reactants, they are said to "lie to the _____"left
- 72aA + bB <--->cC + dD
- 73Kc=[C]^c [D]^d
divided by
[A]^a [B]^b - 74What does the value of Kc tell us about a particular reaction? Explain thisIt tells us which direction the equilibrium is lying to.
A high value of Kc means that there is proportionally more products than reactants so the equilibrium lies to the right and the reaction almost goes to completion
a low value of means that there is proportionally more reactants than products so the equilibrium lies to the left and the reaction has barely taken place - 75If Kc is greater than 1, the reaction...Is considered to go almost to completion
- 76If Kc is less than 1, the reaction...hardly proceeds
- 77—
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- International Baccalaureate (IB) Chemistry (7- Equilibrium) Karteikarten am Equilibrium, erstellt von Lizzy Crockatt am 13/05/2017.
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- Lizzy Crockatt
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