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Chemistry > 8 Reaction kinetics + 9 Periodic table > Flashcards

8 Reaction kinetics + 9 Periodic table Flashcards

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1
Q

Rate of reaction

A

the speed at which a chemical reaction takes place and has the units mol dm^3 s^-1

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2
Q

Collision frequency

A

number of collisions per unit time

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3
Q

Catalyst

A

a substance that increases the rate of a reaction without taking part in the chemical reaction by providing the particles an alternative pathway with a lower activation energy

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4
Q

Collision theory

A

States that for a chemical reaction to take place the particles need to collide with each other in the correct orientation and with enough energy

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5
Q

Increase in reaction rate

A
  • When more collisions per unit time take place, the number of particles with energy greater than the Ea increases and this causes an increase in rate of reaction
  • A catalyst will increase the rate by providing the particles an alternative pathway with a lower activation energy
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6
Q

Effect of concentration changes on the rate of reaction

A
  • The more concentrated a solution is, the greater the number of particles in a given volume of solvent
  • An increase in concentration causes an increase in collision frequency and therefore an increase in rate of reaction
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7
Q

Effect of pressure changes on the rate of reaction

A
  • An increase in pressure in reactions that involve gases has the same effect as an increased concentration of solutions
  • When the pressure in increased, the molecules have less space in which they can move which means the number of effective collisions increases due to an increased collision frequency
  • An increase in pressure therefore increases the rate of reaction
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8
Q

How to calculate rate of reaction

A
  • change in amount of reactants or products (mol dm^3)/time (s)
  • Draw tangents to figure this out and to make it even more accurate draw several of them at several points on the graph
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9
Q

Activation energy (Ea)

A
  • the minimum amount of energy required for a chemical reaction to occur/for a collision to be effective
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10
Q

Use Boltzmann distribution to explain significance in activation energy

A
  • In a sample of a substance, a few particles will have very low energy, a few particles will have very high energy and many particles will have energy in between
  • A Boltzmann distribution curve shows that only a small proportion of molecules in the sample have enough energy for an effective collision and for a chemical reaction to take place
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11
Q

Changes in temperature

A
  • When the temperature of a reaction mixture is increased, the particles gain more kinetic energy which causes the particles to move around faster resulting in more frequent collisions
  • The proportion of successful collisions increases, meaning a higher proportion of particles possess the Ea to cause a chemical reaction
  • With higher temperatures the curve flattens and the peak shifts to the right
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12
Q

An increase in temperature causes an increased rate of reaction due to:

A
  • More effective collisions as the particles have more kinetic energy, making them move around faster
  • A greater proportion of the molecules have kinetic energy greater than the Ea
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13
Q

Catalysis

A

process in which the rate of a chemical reaction is increased, by adding a substance called a catalyst

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14
Q

Catalyst

A
  • increases the rate of reaction by providing the reactants with an alternative reaction pathway which is lower in Ea than the uncatalyzed reaction
  • 2 types of catalysts: homogeneous and heterogeneous
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15
Q

Homogeneous

A
  • the catalyst is in the same phase (state) as the reactants
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16
Q

Heterogeneous

A
  • the catalyst is in a different phase (state) than the reactants
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17
Q

Boltzmann distribution curve and catalysts

A
  • Catalyst provides the reactants an alternative pathway that has a lower Ea
  • By lowering the Ea a greater proportion of molecules in the reaction mixture have energy greater than the activation energy
  • The frequency of effective collisions increases
  • The rate of the catalysed reaction increases compared to the uncatalysed reaction
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18
Q

Atomic radius

A

the distance between the nucleus and the outermost electron of an atom

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19
Q

Trend: across the period, the atomic radii decrease, because

A
  • Number of protons (nuclear charge) and the number of electrons increases by 1 every time you go an element to the right
  • Shielding effect is the same as the elements in a period all have the same number of shells
  • As you go across the period the nucleus attracts the electrons more strongly pulling them closer to the nucleus
  • Therefore, atomic radius (and the size of the atom) decreases
20
Q

Ionic radius

A

the distance between the nucleus and the outermost electron of an ion

21
Q

Trend: across the period, the ionic radius decreases, because

A
  • metals produce + charged ions (cations) and non-metals produce - charged ions (anions)
  • cations have lost their valence electrons and are therefore smaller than parent atoms
  • as there are less electrons there is less shielding of the outer electrons
  • cations Na+ to Si 4+ the ions get smaller due to an increase in nuclear charge attracting the outer electrons in the 2nd principal quantum shell
  • anions are larger than original parent atoms as they have gained an electron which increases the repulsion between electrons , while the nuclear charge remains the same (electron cloud spreads out)
  • p3- to Cl- the ionic radius decreases as nuclear charge increases and fewer electrons are gained
22
Q

Melting point trend:

A
  • general increase in m.p for the period 3 elements up to silicon (has the highest m.p)
  • after silicon the melting point of the elements decrease significantly
23
Q

Electrical conductivity trend:

A
  • across the period, the general trend for electrical conductivity of the elements decreases significantly.
  • It increases from Na to Al and then decreases for the other elements
24
Q

Variations in melting point in terms of the structure and bonding of the elements

A

Why melting point increases from Na-Al
Si has the highest melting point
Why the melting point decreases from P-Ar

25
Q

Why melting point increases from Na-Al

A
  • Na, Mg and Al are metallic elements which form positive ions arranged in a giant lattice in which ions are held together by a sea of delocalised electrons (those from the valence shell) around them.
  • Na will donate one electron into the sea, Mg two electrons and Al three electrons and as a result of this the metallic bonding in Al is stronger than in Na.
  • It is stronger because the electrostatic forces between the 3+ ion and the larger number of negatively charged delocalised electrons is much larger compared to a 1+ ion and the smaller number of delcoalsied electrons in Na.
26
Q

Why Si has the highest melting point

A

due to its giant molecular structure in which each Si atom is held to its neighboring Si atoms by strong covalent bonds

27
Q

Why the melting point decreases from P-Ar

A
  • P, S, CI, Ar are non-metallic elements and exist as simple molecules
  • The covalent bonds within the molecules (intramolecular forces) are strong, but between the molecules (intermolecular forces) are weak instantaneous dipole-induced dipole forces and it therefore doesn’t take much energy to break them
28
Q

Melting point from the highest to lowest: S8 > P4 > CI2 > Ar

A

Sulfur has a larger electron density therefore it has a stronger instantaneous dipole-induced dipole forces

29
Q

Variations in electrical conductivity in terms of the structure and bonding of the elements

A

Na-Al (why it increases as it generally decreases across a period)
Why Si and p are not good conductors

30
Q

Na-Al

A
  • There is an increase in the number of valence electrons that are donated to the sea of delocalized electrons
  • Because of this, in Al there are more electrons available to move around and conduct electricity which makes Al the better conductor than Na
31
Q

Why Si and p are not good conductors

A
  • Si is a giant molecular structure and therefore has no delocalized electrons that can move freely within the structure
  • Therefore, it is not a good electrical conductor and is classified as a semimetal
  • P and S cant conduct electricity due to the lack of delocalized electrons
32
Q

Period 3 elements with oxygen

A

Metal/non-metal + oxygen → metal oxide
4Al (s) + 3O2 (g) → 2Al2O3 (s)
4P (s) + 5O2 (g) → P4O10 (s)

Exception:All produce a solid except for sulfur (g)

33
Q

Period 3 elements with chlorine

A

Metal + chlorine → metal chloride (vigorous)
Non-metal + chlorine → non-metal chloride (slow)

2Al (s) + 3CI2 (g) → Al2CI6 (s)
Si (s) + 2CI2 (g) → SiCI4 (l)
- Non-metals form a liquid product

34
Q

Sodium with water

A

2Na (s) + 2H2O (I) → 2NaOH (aq) + H2 (g)
- Vigorous with cold water
- Forms strong alkaline solution (pH 14)

35
Q

Magnesium with water

A

Mg (s) + 2H2O (I) → Mg(OH)2 (aq) + H2 (g)
- Slow with cold water

Mg (s) + H2O (g) → MgO (s) + H2 (g)
- Vigorous with steam
- Forms weak alkaline solution (pH 11)

36
Q

Period 3 non-metal oxides with water

A

Non-metal oxide + water → depends (H + water =H2 gas and aq H ions, Cl + water= HCI + hypochlorous acid, S + water=sulforous acid + sulfuric acid)

P4O10 (s) + 6H2O (I) → 4H3PO4 (aq) (weak acid 3-4)

Sulfur can produce 2 products:
SO2 (g) + H2O (I) → H2SO3 (aq)
SO3 (g) + H20 (I) → H2SO4 (aq)
- both are strong acids (1-2)

Exception:
Al2O3 and SiO2 have no reaction, insoluble in water

37
Q

Acid/base behaviour of period 3 oxides and hydroxides

A

Metal oxide (basic) + acid → salt + water
Non-metal oxide (acidic) + base → salt + water
*both are neutralization reaction

38
Q

Exception: Al2O3

A

Al2O3 (s) + 3H2SO4 (aq) → Al2(SO4)3 (aq) + 3H2O (I)
Al2O3 (s) + 2NaOH (aq) + 3H2O (I) → 2NaAl(OH)4 (aq)

  • AI2O3 is amphoteric therefore it can be an acid or a base
39
Q

Exception: SO2/SO3

A

SO2 (g) + 2NaOH (aq) → Na2SO3 (aq) + H20 (I)

SO3 (g) + 2NaOH (aq) → Na2SO4 (aq) + H2O (I)

40
Q

Sodium and magnesium (ionic bonding)

A

Produces alkaline solutions and becomes hydroxide ions

Na2O (aq) + H2O (I) → 2NaOH (aq)
O (aq) + H2O (I) → 2OH (aq)

41
Q

Oxides of P and S (covalent bonding)

A

Produce acidic solutions which donate H+ ions to water

Non-metal oxide + water → acid
SO3 (g) + H2O (I) → H2SO4 (aq)

Metal oxide + water → metal hydroxide (basic)

42
Q

Period 3 hydroxides with acid

A

Metal hydroxide + acid → salt + water

Mg(OH)2 (s) + 2HCI (aq) → MgCI2 (aq) + 2H2O (I)

43
Q

Al(OH)3 (amphoteric)

A

Al(OH)3 (s) + 3HCI (aq) → AlCI3 (s) + 3H2O (I)

Al(OH)3 (s) + NaOH (aq) → NaAl(OH)4 (aq)

44
Q

Chlorides react with water to give off?

A

white fumes of hydrogen gas

45
Q

Going across period 3, their chlorides and oxides become…

A
  • more covalent and their structure shifts from a giant ionic to a simple molecular structure
  • Their reactions with water become more vigorous as a result of this as it becomes easier to hydrolyse the chlorides oxides

Chemistry (17 decks)

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