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Chemistry > Chemical Changes and Structure > Flashcards

Chemical Changes and Structure Flashcards

1
Q

What are the 3 conditions of a successful reaction?

A
  1. The reacting particles must collide
  2. The reacting particles must collide with sufficient energy to produce a product
  3. The reacting particles must collide with the correct collision geometry
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2
Q

What 4 factors can increase the rate of a reaction?

A
  1. Decrease in particle size
  2. Increase in temperature
  3. Increase in concentration
  4. Addition of a catalyst
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3
Q

Why does decreasing the particle size lead to an increased rate of reaction?

A

The smaller the particle size, the larger the surface area. The more surfaces there are the more collisions can take place, therefore increasing the reaction rate.

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4
Q

Why does increasing the concentration lead to an increased rate of reaction?

A

The higher the concentration, the higher the number of molecules there are present and available for collisions. Therefore, collisions occur more frequently and the reaction goes faster.

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5
Q

What is the MAIN reason that increasing the temperature leads to an increased rate of reaction?

A

At higher temperatures, more particles have energy equal to the activation energy. Therefore, more successful collisions take place and the reaction goes faster.

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6
Q

Roughly, how much will the temperature have to increase for the reaction rate to double?

A

10°C

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7
Q

Why does the addition of a catalyst lead to an increased rate of reaction?

A

They lower the activation energy. Therefore, successful collisions occur more easily and more frequently and the reaction goes faster.

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8
Q

What is the rate of reaction formula?

A

Average rate = change in quantity / change in time

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9
Q

What is a clock reaction?

A

A reaction where a specific, observable change occurs after a predictable length of time.

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10
Q

What is enthalpy (H)?

A

The measure of the energy stored in a chemical.

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11
Q

What is the formula for calculating the enthalpy change?

A

ΔH = Hproducts - Hreactants

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12
Q

How does the Ea relate to the speed of the reaction?

A

The higher the Ea the higher the barrier and the slower the reaction.

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13
Q

What is an activated complex?

A

An unstable intermediate in which old bonds are partially broken and new bonds are partially formed.

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14
Q

What is the formula for calculating the relative rate?

A

Rate = 1/t

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15
Q

what is the formula for calculating the reaction time?

A

1/rate

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16
Q

What is activation energy?

A

The minimum kinetic energy that colliding molecules must have in order for a reaction to occur.

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17
Q

What is an activated complex?

A

An unstable intermediate in which old bonds are partially broken and new bonds are partially formed.

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18
Q

What is temperature?

A

A measure of the average kinetic energy of the particles in a substance.

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19
Q

What are the two types of catalyst and how are they different?

A

Homogenous - catalysts which are in the same state as the reactants.
Heterogenous - catalysts which are in a different state to the reactants.

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20
Q

What is a catalyst?

A

A substance which speeds up a chemical reaction and remains unchanged at the end.

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21
Q

How do catalysts work?

A

They provide an alternative reaction pathway which has a lower activation energy.

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22
Q

Which group of the periodic table contains unreactive non-metals which are gases at room temperature?

A

Group 8.

23
Q

Which group of the periodic table contains very reactive coloured non-metals?

A

Group 7.

24
Q

Which group of the periodic table contains fairly reactive metals?

A

Group 2.

25
Q

Which group of the periodic table contains very reactive metals which are usually stored under oil to prevent reaction with oxygen and water vapour in the air?

A

Group 1.

26
Q

Why do elements in the same group have similar chemical properties?

A

They have the same number of outer electrons.

27
Q

How does metallic bonding work?

A

Atoms lose their outer electrons to a common ‘pool’ of delocalised electrons. As each atom has lost one or more electrons, the atoms become positively charged ions. The charged metal ions are now attracted to the pool of electrons.

28
Q

Why do metals have a lustre?

A

The delocalised electrons absorb energy from light and the re-emit it.

29
Q

How strong is metallic bonding?

A

Quite strong.

30
Q

Describe covalent molecular structures.

A

They consist of groups of small numbers of atoms joined by covalent bonds.

31
Q

What intermolecular force are covalent molecular elements often held together by?

A

London Dispersion Forces.

32
Q

Which three discreet covalent molecular substances have slightly higher melting points due to their unique structures?

A

Sulphur - can form closed, eight membered, puckered rings.
Phosphorous - forms tetrahedral molecules.
Fullerenes - discrete, covalently bonded molecules of carbon.

33
Q

Describe covalent network elements.

A

Huge complex structures where each atom is covalently bonded to other atoms. Covalent network structures consist of many thousands of atoms bonded together by covalent bonds.

34
Q

What are the four covalent network structures?

A
  1. Carbon diamond
  2. Carbon graphite
  3. Boron
  4. Silicon
35
Q

What is covalent radius?

A

Half the distance between the nuclei of 2 bonded atoms.

36
Q

How does atomic radius change as you go across a period?

A

It decreases.

37
Q

How does atomic radius change as you go down a group?

A

It increases.

38
Q

Why does atomic radii increase as you go down a group?

A

As you go down a group the number of energy levels increases and this causes a shielding effect between the outer electrons and the nucleus.

38
Q

Why does atomic radii decrease as you go down a group?

A

As you go across a period the nuclear charge increases due to the fact that protons are being added. This exerts an increasing attraction on the outermost electrons which pulls them closer to the nucleus.

38
Q

What is electronegativity?

A

A measure of the attraction an atom involved in a bond has for the electrons of the bond.

38
Q

What is first ionisation energy?

A

The energy required to remove one mole of electrons from one mole of atoms.

38
Q

In what state must ionisation take place?

A

Gaseous.

38
Q

What is the equation for the first ionisation of chlorine?

A

Cl(g) -> Cl+(g) + e-

39
Q

What is the equation for the second ionisation of chlorine?

A

Cl+(g) -> Cl2+(g) + e-

40
Q

How does the 1st ionisation energy change as you go down a group?

A

It decreases.

41
Q

How does the 1st ionisation energy change as you go across a period?

A

It increases.

42
Q

Describe ionic bonding.

A

The attraction between positive and negative ions.

43
Q

What are the 3 Van der Waal’s forces?

A
  1. London dispersion forces
  2. Permanent dipole-permanent dipole attractions
  3. Hydrogen bonding
44
Q

What are London dispersion forces?

A

Temporary, weak electrostatic attractions between the positive end of a temporary dipole and the negative end of another. The weakest type of Van der Waal’s attraction.

45
Q

How does covalent radius affect the MP/BP of an element?

A

As the covalent radius increases the MP/BP also increases.

46
Q

Describe covalent bonding.

A

The covalent bond is a result of two positive nuclei being held together by their common attraction for the shared pair of electrons.

47
Q

Describe polar covalent bonding.

A

Polar covalent bonds are formed when the attraction of the atoms for the pair of bonding electrons is different.

48
Q

Describe ionic bonding

A

Ionic bonds are the electrostatic attraction between positive and negative ions. Ionic compounds form lattice structures of oppositely charged ions.

Chemistry (2 decks)

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