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Chemical reactivity Flashcards

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1
Q

Describe how to change the rate of a chemical reaction
(4)

A
  • Increasing the concentration of reactants
  • Increasing the temperature of the reaction system
  • Increasing the surface area of a solid reactant
  • Adding a catalyst to the reaction
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2
Q

Define the term activation energy

A

the minimum amount of energy required for a reaction to occur.

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3
Q

Define the term catalyst

A

A substance that increases the rate of a reaction without itself being consumed.

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4
Q

Recognise the role of catalysts in providing an alternate reaction pathway

A

Catalysts enable a reaction to occur faster by providing an alternative reaction pathway with a lower activation energy.

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5
Q

Collision theory

A

Inorder for a reaction to occur between two particles, the particles must collide with each other with sufficient energy to break bonds and form new ones.

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6
Q

How concentration affects rate of reaction:

A

Increased concentration brings about an increase in the frequency of collisions, so more particles react to give products.

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7
Q

How surface area affects rate of reaction:

A

Increase in surface area exposes more reactant particles to collisions. Therefore the collision frequency increases. More successful collisions will occur per second and hence a faster rate of reaction.

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8
Q

How temperature affects the rate of reaction:

A

Increase in temperature gives more kinetic energy to the particles. This means that the particles start moving faster which leads to increase in collision frequency. A larger proportion of colliding particles with sufficient energy to overcome the activation energy.

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9
Q

How Catalyst affects the rate of reaction:

A

A catalyst speeds up the rate of reaction by providing an alternative path of lower activation energy. As a result, a larger proportion of reactant particles now have sufficient energy to overcome the activation energy. This leads to increase in collision frequency and the number successful collisions per second.

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10
Q

Temperature changes the kinetic energy of the particles, not….

A

the activation energy.

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11
Q

Chemical equilibrium

A

the state reached by a reaction mixture when the rates of the forward and reverse reactions have become equal.

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12
Q

Completion reaction

A

when one of the reactants is completely used up.

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13
Q

Describe the dynamic nature of equilibrium.

A

consists of a forward reaction, in which substances react to give products and a reverse reaction, in which products react to give the original reactants.

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14
Q

The equilibrium-constant expression for a reaction is obtained by

A

multiplying the concentrations of products, dividing by the concentrations of reactants, and raising each concentration to a power equal to its coefficient in the balanced chemical equation.

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15
Q

how to calculate values for equilibrium constants

A
  • Substituting the value of the concentrations of products and reactants into equilibrium constant expressions.
  • The concentrations of pure solids and liquids are always considered to be “1” and therefore, do not appear in the equilibrium expression.
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16
Q

If the value of Kc is large (eg Kc is greater than 1)

A

then the position of the equilibrium will favour the right hand side of the reaction. This means that the concentration of products is greater than the reactants. The forward reaction is favoured.

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17
Q

If the value of Kc is small (eg Kc is less than 1 )

A

then the position of the equilibrium will favour of the left hand side of the reaction. This means that the concentration of reactants is greater than the products. The backward reaction is favoured.

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18
Q

Le Chatelier’s principle

A

“When a change is applied to a system at equilibrium, the system responds so that the effects of the change are minimised.”

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19
Q

How does change in Pressure affect Kc value

A

No change to value of Kc

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20
Q

How does Increasing pressure (or decrease in volume) affect position of equilibrium

A

Favours the reaction that produces least number of moles of gas.

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21
Q

How does Decreasing pressure (or increase in volume) affect the position of equilibrium

A

Favours the reaction that produces most number of moles of gas.

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22
Q

How does change in temperature affect the value of Kc in equilibrium

A

Kc will be changed. Favour of reactants = decrease in Kc Favour of products = increase in Kc value.

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23
Q

How does Increasing temperature affect the position of equilibrium

A

Favours the endothermic reaction (heat absorbing △H positive)

24
Q

How does Decreasing temperature affect the position of equilibrium

A

Favours the exothermic reaction (heat producing △H negative)

25
Q

How does change in concentration affect the position of equilibrium

A

If product or reactant is removed, the equilibrium will shift to favour production of the removed species. (replacing the removed species.) No change to value of Kc

26
Q

How does addition of catalyst affect the position of equilibrium

A

Catalyst speeds up both forward and reverse reactions - this causes equilibrium to be established more rapidly. No effect on value of Kc

27
Q

Define acids and bases in terms of proton or hydrogen ion transfer.

A

Acids - are proton donors.
Base - are proton acceptors
*A “proton” is really just a hydrogen atom that has lost its electron Hᐩ

28
Q

Conjugate base

A

When an acid loses a proton

29
Q

Conjugate acid

A

When a base gains a proton

30
Q

Conjugate acid/base pairs are molecules and ions that differ in their structure by…

A

a single proton, Hᐩ

31
Q

write the equilibrium reaction and the equilibrium constant for the dissociated water and identify the equilibrium constant as Kw
(Is a formula)

A

[H3Oᐩ] = [OH⁻] = 1.00 x 10-7 = Kw

32
Q

[H3Oᐩ] = (in terms of OH)

A

[H3Oᐩ] = 1.00 x 10-14 / [OH⁻]

33
Q

[OH⁻] = (in terms of H3Oᐩ

A

[OH⁻] = 1.00 x 10-14 / [H3Oᐩ]

34
Q

Define and measure pH.

A

A measure expressing the acidity or alkalinity of a solution. 7 = neutral. Less than 7 = Acidic. More than 7 = alkaline. Can be measured by universal indicator.

35
Q

pOH = (hint terms of OH)

A

pOH = -log[OH⁻]

36
Q

Calculating the [H3Oᐩ] with pH formula

A

10^-pH

37
Q

Calculating the [H3Oᐩ] with log and pH

A

shift log - pH

38
Q

Calculating the pH of strong acids with pH

A

pH = -log[H3Oᐩ]

39
Q

Strong acids and conductivity

A

Strong acids donate protons readily in aqueous solution to become completely ionised. High concentration of ions means great electrical conductor.

40
Q

Weak acids and conductivity

A

Weak acids donate protons to a limited extent in aqueous solution, so are only partially ionised or dissociated in water. Low concentration of ions means poor electrical conductor.

41
Q

Strong base and conductivity

A

Strong bases dissociate completely in water to form OH⁻ ions. High concentration of ions means great electrical conductor.

42
Q

Weak base and conductivity

A

Weak acids partially dissociate in water and these few ions react with water. Low concentration of ions means poor electrical conductor.

43
Q

Weak acid reaction with water concentration

A

weak acid doesn’t dissociate completely. Double arrow in reaction. Therefore lower concentration of [H3Oᐩ]

44
Q

Strong acid reaction with water concentration

A

Strong acid dissociate completely. Single arrow in reaction. Higher concentration of [H3Oᐩ]

45
Q

Weak base reaction with water concentration

A

Weak bases does not dissociate completely. Double arrow in reaction. Therefore lower concentration of [OH-]

46
Q

Strong base reaction with water concentration

A

Strong base dissociate completely. Single arrow in reaction. Lower concentration of [OH-]

47
Q

Effect of dilution on a weak acid in aqueous solution.

A

Decrease in concentration of [H3Oᐩ] causes increase in pH of solution.

48
Q

acid- base properties of ionic compounds (salts) that change the pH of water. - acidic salts

A

acid donates a hydrogen to water, forming hydronium ions. Increase in concentration of hydronium ions causes the pH of solution decreases.

49
Q

acid- base properties of ionic compounds (salts) that change the pH of water. - basic salts

A

base accepts a hydrogen from water, forming hydroxide ions. Increase in hydroxide ions, causes the pH of solution to decrease.

50
Q

acid- base properties of ionic compounds (salts) that change the conductivity of water. - acidic salts

A

Acidic salts are ionic compounds that dissolve in water when added to water it forms ions. As concentration of ions is high the solution will be a good conductor of electricity.

51
Q

Properties of ionic compounds (salts) that change the conductivity of water.

A

Basic salts dissolve in water, dissociating into its ions. Due to high concentration of ions solution will be a good conductor of electricity.

52
Q

Strong acidic/ basic solution

A

Dissociate completely into their ions in aqueous solution

53
Q

Weak acidic/basic solutions

A

Do not completely dissociate into their ions in aqueous solution.

54
Q

Concentrated acid solutions

A

Contains more [H3Oᐩ] within the same volume than a dilute acid

55
Q

Concentrated base

A

Contains more [OH-] within the same volume than a dilute base.

56
Q

Explain why equal amounts of monoprotic strong and weak acids will neutralise the same amount of a given base

A

Because during this neutralisation reaction the pH will approach pH 7, as equal concentrations of [OH-] and [H3Oᐩ] are produced.

Chemistry (3 decks)

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