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ZZ Chem 2 > the rate and extent of chemical change > Flashcards

the rate and extent of chemical change Flashcards

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1
Q

Define rate of reaction

A
  • How fast the reactants are changed into products
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2
Q

Name the equation used to calculate/measure the rate of reaction

A
  • Rate of reaction = amount of reactant used / Time
  • Rate of reaction = amount of product formed / Time
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3
Q

What can the quantity of reactant or product be measured by?

A
  • Mass in grams or volume in cm3
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4
Q

What are the units of rate of reaction?

A
  • g/s or cm3/s
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5
Q

What are the units for rate of reaction in terms of moles?

A
  • You can also use quantity of reactants in terms of moles (instead of mass or volume) and therefore, units for rate of reaction in mol/s
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6
Q

How do you find the rate of reaction graphically?

A
  • To measure the rate of reaction: draw tangents to curves and use the slope of the tangent
  • Calculate the gradient of a tangent to the curve on these graphs as a measure of rate of reaction at a specific time
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7
Q

Describe the relationship between the gradient of the line and the rate of reaction

A
  • The steeper the line on the graph, the faster the rate of reaction
  • Over time the line becomes less steep as the reactants are used up
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8
Q

Name the factors which affect the rates of chemical reactions

A
  • Concentration
  • Pressure
  • Surface area
  • Temperature
  • Catalysts
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9
Q

What does the rate of a chemical reaction depend on?

A
  • Collision frequency of reacting particles
  • Energy transferred during a collision
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10
Q

Define collision theory

A
  • Chemical reactions can occur only when reacting particles collide with each other and with sufficient energy
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11
Q

Define activation energy

A
  • The minimum amount of energy that particles must have to react
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12
Q

What happens when you increase the concentration of reactants in solution?

A
  • If a solution is more concentrated, it means there are more particles in the same volume of water
  • This means that the same number of particles occupy a smaller space
  • Increases the frequency of collisions and so increases the rate of reaction.
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13
Q

What happens when you increase the pressure of reacting gases?

A
  • If pressure increases, it means there are more particles in the same volume of gas
  • This means that the same number of particles occupy a smaller space
  • Increases the frequency of collisions and so increases the rate of reaction
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14
Q

What happens when you increase the surface area of solid reactants?

A
  • When you break up a solid into smaller pieces it will increase its SA:V ratio
  • This means for the same volume of solid, the particles have more area to work on
  • Increases the frequency of collisions and so increases the rate of reaction.
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15
Q

What happens when you increase the temperature of the reactants?

A
  • When the temp increases, the particles move faster (gain kinetic energy)
  • Increases the frequency of collisions and makes the
    collisions more energetic, and so increases the rate of reaction.
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16
Q

Define a catalyst

A
  • Catalysts are substances that speed up chemical reactions without being changed or used up during the reaction
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17
Q

Define an enzyme

A
  • Enzymes act as catalysts in biological systems
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18
Q

Are catalysts included in the equation for a reaction?

A
  • No, catalysts are not included in the equation for a reaction
19
Q

What is the purpose of a catalyst?

A
  • Decrease the activation energy; this increases the proportion of particles with energy to react
  • Provide a different pathway for a chemical reaction that has a lower activation energy.
20
Q

What is a reversible reaction?

A
  • Where in​ ​some​ ​chemical​ ​reactions,​ ​the​ ​products​ ​of​ ​the​ ​reaction​ ​can​ ​react​ ​to​ ​produce the​ ​original​ ​reactants
  • The​ ​direction​ ​of​ ​the​ ​reaction​ ​can​ ​be​ ​changed​ ​by​ ​changing​ ​the​ ​conditions
    (e.g.​ ​for​ ​forwards​ ​reaction​ ​use​ ​hot​ ​conditions​ ​and​ ​for​ ​reverse​ ​use​ ​cool)
21
Q

Describe what happens in a reversible reaction

A
  • As the reactants react, their concentrations fall, so the forward reaction will slow down
  • But as more products are made, and their concentrations rise. the backwards reaction will speed up
  • After a while, the forward reaction will be at the same rate as the backwards causing equilibrium
22
Q

What happens if a reversible reaction is at equilibirum?

A
  • There is no overall effect
  • The concentrations of reactants and products have reached a balance and won’t change
23
Q

What symbol is used in a reversible reaction?

A
  • Use​ ​the​ ​symbol​ ​⇌​ ​instead​ ​of​ ​→​ ​to​ ​represent​ ​a​ ​reversible​ ​reaction
24
Q

Give an example of a reversible reaction

A
  • ​The​ ​Haber​ ​Process:​ ​hydrogen​ ​+​ ​nitrogen​ ​⇌​ ​ammonia
25
Q

What happens if the equilibrium of a reversible reaction lies to the right?

A
  • The conc of products is greater than reactants
26
Q

What happens if the equilibrium of a reversible reaction lies to the left?

A
  • The conc of the reactants is greater
27
Q

Describe the energy changes in a reversible reaction

A
  • If​ ​a​ ​reversible​ ​reaction​ ​is​ ​endothermic​ ​one​ ​way,​ ​it​ ​is​ ​exothermic​ ​in​ ​the​ ​opposite direction.
  • The​ ​same​ ​amount​ ​of​ ​energy​ ​is​ ​transferred​ ​each​ ​way​ ​(just​ ​for​ ​one​ ​the​ ​energy​ ​will be​ ​lost​ ​and​ ​for​ ​the​ ​other​ ​the​ ​same​ ​amount​ ​will​ ​be​ ​gained)
  • The energy transferred from the surrounding by the endothermic reaction is equal to the energy transferred to the surroundings during the exothermic reaction
28
Q

Give an example of endothermic and exothermic in reversible reactions

A
  • Thermal decomposition of hydrated copper sulfate
  • hydrated copper sulfate <> anhydrous copper sulfate + water
  • If you heated blue hydrated copper sulfate crystals, it drives the water off and leaves WHITE anhydrous copper sulfate powder (endothermic)
  • If you add water to the white powder, you get blue crystals (exothermic)
29
Q

When is equilibrium reached in a reaction?

A
  • When​ ​a​ ​reversible​ ​reaction​ ​occurs​ ​in​ ​a​ ​closed​ ​system,​ ​equilibrium​ ​is​ ​reached when​ ​the​ ​reactions​ ​occur​ ​at​ ​exactly​ ​the​ ​same​ ​rate​ ​in​ ​each​ ​direction.
30
Q

Explain Le Chatelier’s principle

A
  • The​ ​relative​ ​amounts​ ​of​ ​all​ ​the​ ​reacting​ ​substances​ ​at​ ​equilibrium​ ​depend​ ​on the​ ​conditions​ ​of​ ​the​ ​reaction.
  • If​ ​a​ ​system​ ​is​ ​at​ ​equilibrium​ ​and​ ​a​ ​change​ ​is​ ​made​ ​to​ ​any​ ​of​ ​the​ ​conditions, then​ ​the​ ​system​ ​responds​ ​to​ ​counteract​ ​the​ ​change​
31
Q

What does the position of equilibrium depend on?

A
  • Pressure
  • Temp
  • Concentration
32
Q

What is the effect of changing concentration on equilibrium in a reversible reaction?

A
  • I​f ​the​ ​concentration​ ​of​ ​one​ ​of​ ​the​ ​reactants​ ​or​ ​products​ ​is​ ​changed,​ ​the​ ​system is​ ​no​ ​longer​ ​at​ ​equilibrium​ ​and​ ​the​ ​concentrations​ ​of​ ​all​ ​the​ ​substances​ ​will change​ ​until​ ​equilibrium​ ​is​ ​reached​ ​again.
33
Q

What happens if the concentration of reactants is increased in a reversible reaction?

A
  • If​ ​​concentration​ ​of​ ​reactants​ ​is​ ​increased​:​ ​position​ ​of​ ​equilibrium​ ​shifts towards​ ​products​ ​so​​ ​more​ ​product​ ​is​ ​produced​​ ​until​ ​equilibrium​ ​is​ ​reached again
  • (decrease reactants by making more product)
34
Q

What happens if the concretion of products is increased in a reversible reaction?

A
  • If​ ​​concentration​ ​of​ ​products​ ​is​ ​increased​:​ ​position​ ​of​ ​equilibrium​ ​shifts​ ​towards reactants​ ​so​ ​​more​ ​reactant​ ​is​ ​produced​​ ​until​ ​equilibrium​ ​is​ ​reached​ ​again
35
Q

What happens if the concentration of products is decreased in a reversible reaction?

A
  • System tries to increase it again by reducing the amount of reactants
36
Q

What happens if the temperature is increased equilibrium in a reversible reaction?

A
  • If​ ​​temperature​ ​is​ ​increased​:​ ​equilibrium​ ​moves​ ​in​ ​the​ ​​direction​ ​of​ ​the endothermic​ ​reaction​​ ​(e.g.​ ​if​ ​forwards​ ​reaction​ ​is​ ​endothermic​ ​and temperature​ ​is​ ​increased,​ ​equilibrium​ ​shifts​ ​right​ ​to​ ​produce​ ​more​ ​product)
  • To decrease the heat, meaning more products for endothermic and fewer for exothermic
37
Q

What happens if the temperature is decreased in a reversible reaction?

A
  • If​ ​​temperature​ ​is​ ​decreased​:​ ​equilibrium​ ​moves​ ​in​ ​the​ ​​direction​ ​of​ ​the exothermic​ ​reaction to produce more heat
  • You will get more products for exothermic and fewer for endothermic
38
Q

For an exothermic reaction, what happens when you increase/decrease the temperature?

A
  • An​ ​increase​ ​in​ ​temperature - decreases​ ​yield​ ​of​ ​reaction
  • A​ ​decrease​ ​in​ ​temperature - increases​ ​yield​ ​of​ ​reaction
39
Q

For an endothermic reaction, what happens when you increase/decrease the temperature?

A
  • An increase in temperature - increases​ ​yield​ ​of​ ​reaction
  • A decrease in temperature - decreases​ ​yield​ ​of​ ​reaction
40
Q

What is the effect of pressure changes on equilibrium in a reversible reaction?

A
  • In​ ​gaseous​ ​reactions,​ ​an​ ​increase​ ​in​ ​pressure​ ​will​ ​favour​ ​the​ ​reaction​ ​that produces​ ​the​ ​least​ ​number​ ​of​ ​molecules​ ​as​ ​shown​ ​by​ ​the​ ​symbol​ ​equation​ ​for
    that​ ​reaction.
41
Q

What happens if pressure is increased in a reversible reaction?

A
  • If​ ​​pressure​ ​is​ ​increased​:​ ​equilibrium​ ​shifts​ ​to​ ​​side​ ​of​ ​equation​ ​with​ ​fewer​ ​moles of​ ​gas​
    ​(e.g.​ ​N​2​​ ​+​ ​3H2​ ​​ ​​⇌​ ​​2NH​3,​ ​ ​left​ ​side​ ​has​ ​4​ ​moles​ ​of​ ​gas​ ​(1+3)​ ​and​ ​right​ ​has​ ​2 moles​ ​of​ ​gas.​ ​If​ ​you​ ​increase​ ​the​ ​pressure​ ​equilibrium​ ​moves​ ​right​ ​as​ ​there​ ​are fewer​ ​moles​ ​of​ ​gas​ ​on​ ​the​ ​right​ ​hand​ ​side,​ ​making​ ​more​ ​product)
42
Q

What happens if pressure is decreased in a reversible reaction?

A
  • If​ ​​pressure​ ​is​ ​decreased​:​ ​equilibrium​ ​will​ ​shift​ ​to​ ​​side​ ​of​ ​equation​ ​with​ ​more moles​ ​of​ ​gas​​ ​(e.g.​ ​for​ ​previous​ ​example​ ​equilibrium​ ​would​ ​move​ ​left
43
Q
A

If​ ​a​ ​reaction​ ​produces​ ​a… An​ ​increase​ ​in​ ​pressure…
A​ ​decrease​ ​in​ ​pressure…
…larger​ ​volume​ ​of​ ​gas​ ​(more​ ​moles) Decreases​ ​yield​ ​of​ ​reaction
Increases​ ​yield​ ​of​ ​reaction
…smaller volume of gas (fewer moles)
Increases​ ​yield​ ​of​ ​reaction Decreases​ ​yield​ ​of​ ​reaction

ZZ Chem 2 (5 decks)

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