Equilibria Flashcards | Knowt (2024)

Explain why the concentrations of the reactants and the products remain constant when equilibrium is established.

Because the rate of forward reaction = rate of backward
reaction

Give one disadvantage of using temperatures much higher than 1000 °C.

Cost (of energy) is high/ expensive/ amount
of energy is high

Explain why the addition of a catalyst has no effect on the equilibrium yield of hydrogen in the reaction.

Changes/ speeds up/ increases the rate of
both the forward and backward reactions equally

Explain why the shaded area is very small.

Because (very) few/ small no of molecules have high
energy/ energy greater than Ea

Area under curve?

Area under curve represents (total) number/amount of molecules

Describe how the shape of the curve, the area under the curve, the value of Ea and the value of Q change if the temperature is increased.

1. Curve becomes flatter /lower and shifts to right
2. Area does not change
3. Ea does not change
4. Q is higher / increases/ to the right

Explain why a small increase in temperature results in a large increase in the rate of a
reaction.

Increasing temp largely increases rate because there are MANY MORE molecules/collisions with energy greater than the activation energy
= More successful collisions
= More collisions with energy greater than the activation energy

Explain why a catalyst increases the rate of a reaction.

1. (alternative route) Catalyst lowers activation energy
2. More molecules have energy greater than the activation energy
3. More successful collisions

State and explain the effect of increasing the pressure on the equilibrium yield of hydrogen iodide.

No effect
Same no of moles on each side / each side affected equally

Explain why collisions between molecules of A and B do not always lead to a reaction.

Particles A and B may not have the activation energy required for a successful collision

Explain why increasing the temperature by a small amount has a much bigger effect on the rate of reaction than increasing the pressure by a small amount.

1. Increasing temperature by a small amount increases the number of particles having E ≥ Ea 1
2. Increasing pressure by a small amount increases collisions by a small amount

Explain what is meant by a reaction in equilibrium

Rate of the forward reaction = rate of the backward reaction
Concentrations are constant

An increase in temperature causes a decrease in the yield of Z. State and explain what
can be deduced about the enthalpy change for the forward reaction.

= Negative/endothermic
= the equilibrium shifts to decrease
the temperature/ oppose the increase in
temperature

Use the equations for Processes 1, 2 and 3 to show why it can be claimed that there is no net emission of carbon-containing greenhouse gase

6 moles either side = same in, same out

Use Le Chatelier's principle to suggest and explain the effect on the yield of zinc oxide
of allowing the carbon dioxide to escape from the container

The yield of zinc oxide increases/ greater
Removal of the carbon dioxide results in the equilibrium
Shifting / moving / goes to the right / L to R
favours the forward reaction/ towards the products
(By Le Chatelier's principle) the reaction/
equilibrium will respond so as to replace the CO2 / lost product / oppose decrease in conc of CO2

Why is process 3 more environmentally friendly?

Process 3 avoids the release of SO2
Because it captures SO2 and converts is to H2SO4
SO2 BAD = toxic, contributes to acid rain

State the effect on the activation energy of increasing the temperature.

NONE

Explain why reactions involving gases become faster as the temperature increases

More molecules have energy greater than the activation energy
Therefore there are more successful collisions

State what is meant by dynamic equilibrium

Rate of forward reaction = rate of backward reaction (1)
Concentration of reactants and products are constant

Dec temp, as well as reverse reaction is endo you say

Reaction is exothermic

What causes some molecules to have very low energies?

Collisions cause some molecules to slow down/lose energy

Why does a very small percentage of collisions lead to reaction

Only a small percentage of collisions have energy greater than the activation energy

State how proportion of successful collisions between molecules can be increased

Use a catalyst = lowers activation energy = more molecules/collisions have energy greater than the activation energy

State the advantage of using a temp lower than 800K
State advantage of using a temp higher than 800k
Hence explain why 800K is referred to as a compromise temperature

= Yield of (product) increases
= Faster ROR
= Balance between rate and yield

Why is a high temp batch process less energy efficient than a high temp continuous one?

= Batch process involves stopping and starting
= Energy lost when it cools down after stopping or energy needed to heat up each time

Explain why increasing the pressure increases the ROR

1. More molecules in a given volume
2. Higher frequency of collisions
3.

Small inc in temperature = large increase in rate of reaction

MANY more molecules have energy greater than the activation energy

Meaning of the term catalyst

Speeds up reaction, chemically unchanged at the end

Why are solid catalysts given in the form of powder

INC SURFACE AREA

Increase temp

endothermic reaction FAVOURED

What must happen before molecules of A react to form molecules B + C

1. They must collide
2. With energy greater than activation energy
3. And with CORRECT ORIENTATION

Why does the concentration of A remain constant after some time?

1. EQUILIBRIUM REACHED = NET CONCS OF P + R REMAIN CONSTANT
2. RATE OF FORWARD REACTION = RATE OF REVERSE REACTION

Why does conc of A fall to a low value if temp is increased?

1. Reaction is endothermic
2. Forward reaction is endothermic
3. Shifts L to R

Explain why the rate of this reaction decreases with time

1. Fewer collisions
2. Reactants used up

Why is an increased temp required when there is no catalyst?

1. TO SPEED UP REACTION

Why does bromine not react with aqueous chlorine ions

Weaker reducing agent than Cl2

Half equation for reduction of chlorine in reaction with water

Cl2 + 2H2O -> 2HClO + 2H+ + 2e-

State how you would use the curve to find the rate of reaction at point A

Gradient (or slope)

RORS

100 cm of 1.0 mol dm solution is slower, but comes to the same volume as a 2.0 mol dm solution 50 cm

RORS

25cm of 2.0 mol dm = steeper than the original, but volume comes to half!!!

Why do these reactions suggest H2O2 is behaving as a catalyst?

1. Remains unchanged = not used up in the reaction
2. Offers alternative reaction route

Why is 500k considered a compromise

1. HIGH TEMP REACTION YIELD IS LOW
2. LOW TEMP REACTION RATE IS SLOW
3. Therefore use a BALANCE between rate + yield

Choosing catalyst on a graph, how do you know

1. Yield unchanged
2. Reaction is faster

Activation energy

Minimum energy required for a reaction to occur

Why does a small decrease in temperature lead to a large decrease in the rate of reactions

1. Many fewer molecules were energy greater than the activation energy.

Why do most collisions between gas phase reactants not lead to a reaction

1. Wrong orientation
2. Do not have sufficient energy = not have energy greater than activation energy

1. Add a catalyst = lowers activation energy
2. Increase pressure = increases collision frequency

Le Chatelier's principle

When a system/reaction in equilibrium is disturbed), the equilibrium shifts /moves in a direction which tends to reduce the disturbance

Why does the rate of reaction decrease when the temperature of water in the lake falls

1. Decreases the energy of the energy of the particles
2. Decrease in number of molecules with energy greater than the activation energy.
3. Results in fewer successful collisions

Why must a catalyst be hot?

1. To provide activation energy
2. To provide the minimum energy to make a reaction start

Why does a catalyst remain hot throughout the reaction?

Reaction is exothermic = releases heat

Exothermic

The (forward) reaction is exothermic OR the (forward) reaction releases heat

Use Le Chatelier's principle to explain why the green colour disappears when sodium
hydroxide solution is added to this solution

1. NaOH reacts with the acid(s) / the HCl / the HClO / H+
2. Therefore conc of acid decreases
3. Equilibrium moves to oppose decrease in conc of acid
4. Equilibrium shifts (from left ) to right OR wtte

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