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Higher Chemistry > Unit 1- rate of reaction and periodicity > Flashcards

Unit 1- rate of reaction and periodicity Flashcards

(108 cards)

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1
Q

What 3 things must happen for a chemical reaction to occur?

A

Particles must collide with one another
Particles must collide with sufficient energy
Particles must collide with the correct geometry

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2
Q

What are the two basic ways reaction rates can be increased?

A

Increasing the number of collisions

Increasing the number of particles with the activation energy

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3
Q

How can the number of collisions be increased in a reaction

A 
Increasing...
Surface area
Concentration
Pressure 
Temperature
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4
Q

How can the number of particles with the activation energy be increased?

A

Increasing the temperature

Adding a catalyst

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5
Q

What is concentration

A

The number of particles in a given volume

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6
Q

Explain what happens when the concentration of reacts are increased in a chemical reaction

A

More collisions take place and therefore the reaction is faster due to more successful collisions

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7
Q

What is pressure?

A

How often the gas molecules collide with the walls of a container

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8
Q

How can pressure be increased?

A

Compressing the same number of particles into a smaller volume

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9
Q

How does increasing the pressure increase reaction rate?

A

More collisions take place and therefore there will be more successful collisions

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10
Q

What reacts faster powders or grains?

A

Powders

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11
Q

Why does a decrease in particle size increase the rate of a reaction?

A

There is a larger number of particles on the surface of a solid that are able to take part in collisions

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12
Q

What is temperature?

A

The average kinetic energy of the particles of a substance

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13
Q

Why does increasing temperature increase reaction rate?

A

The reaction particles will have a greater kinetic energy and so collisions between then are more likely to be successful

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14
Q

Increasing temperature means that more particles have…

A

The required activation energy

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15
Q

How do you measure the relative rate of a reaction?

A

1/time taken for the reaction to take place

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16
Q

What is the units for relative rate?

A

s-1

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17
Q

What is a potential energy diagram used for?

A

To show the energy pathway for a chemical reaction

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18
Q

What is enthalpy?

A

The measure of chemical potential energy contained in a substance

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19
Q

What is the symbol for enthalpy?

A

H

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20
Q

What is enthalpy change measured in?

Not one mole

A

kJ

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21
Q

What is enthalpy change measured in?

One mole of a substance

A

kJmol-1

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22
Q

What is the equation for enthalpy change?

A

Enthalpy of products minus enthalpy of reactants

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23
Q

What is an exothermic reaction?

A

A reaction where chemical potential energy is changed into heat energy and heat energy will be lost

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24
Q

What happens to the temperature in an exothermic reaction

A

It will increase

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25
The value of Hp is lower than Hr for an exothermic reaction | True or false
True
26
Enthalpy change of an exothermic reaction is positive | True or false
False
27
What is an endothermic reaction?
A reaction where heat energy is taken in and changed into chemical potential energy
28
What happens to the temperature of an endothermic reaction?
It will decrease
29
The value of Hp is greater than Hr in an endothermic reaction True or false
True
30
The enthalpy change for an endothermic reaction is positive | True or false
True
31
What is activation energy?
The energy required by the colliding molecules to form an activated complex
32
What is an activated complex?
An unstable intermediate with bonds within the reactant molecule beginning to break and new bonds forming to make products
33
What is the symbol for activation energy
Ea
34
Where is the activated complex represented by on a potential energy diagram
At the top of the activation barrier
35
A different activated complex is for in the reverse reaction than the forward reaction True or false
False
36
What do energy distribution diagrams show?
How many particles are moving with each value of kinetic energy
37
How is the activation energy represented on an energy distribution diagram
A dashed line from the X axis
38
On an energy distribution diagram what represents the number of particles which have sufficient energy to react?
The area under the curve to the right of Ea
39
If the temperature of a reaction increases what happens to the number of particles with Ea?
Increases
40
What happens to a catalyst during a reaction?
The catalyst takes part in the reaction but is regenerated at the end of the reaction
41
What do catalyst provide?
An alternative reaction pathway with a lower activation energy
42
What does a catalyst do to the activation energy
Decreases it
43
What does a catalyst do to the energy distribution diagram?
Moves the activation energy line to the left
44
How are the elements in the periodic table arranged?
In order of increasing atomic number
45
What are the vertical columns of the periodic table called?
Groups
46
What are the horizontal rows in the periodic table called
Periods
47
What do all the elements in one group have in common
Chemical properties
48
What is group 0 called
Noble gases
49
How do the noble gases naturally exist
Single, unattached atoms
50
Describe the noble gases outer electron shell
Stable
51
Name the monatomic gases among the first 20 elements
Helium Neon Argon
52
Are the boiling and melting points of monatomic gases high or low
Low
53
Why do monatomic gases have low mp and bp
They are easily separated by overcoming the weak forces of attraction between the atoms
54
What are the forces between monatomic gases?
London dispersion forces
55
Describe a temporary dipole
One side of an atom or molecule becomes slightly negative and slightly positive
56
What will happen to adjacent atoms or molecule to a temporary dipole
Induced dipoles
57
What are London dispersion forces a result of
The electrostatic attractions between temporary dipoles and induced dipole
58
What determine the strength of LDF
The size of the molecule or atom
59
The strength of LDF is proportional to the number of electrons in an atom or molecule True or false
True
60
Why does more electrons lead to stronger London dispersion forces?
More dipoles are established
61
Do the boiling points increase or decrease going down group 0
Increase
62
What other bonding is involved in the noble gases except LDF
There are none
63
Do metals gain electrons easily
No they lose electrons easily
64
What happens to the electrons in metallic ally bonded elements
They become delocalised
65
What is the structure of metal in a solid state?
A lattice
66
What is a metallic lattice made up of
Positive metal ions held together by a sea of delocalised electrons
67
What are metallic bonds
Electrostatic attraction between the positive metal ions and the negative delocalised electrons
68
The delocalised electrons in a metallic lattice cannot move | True or false
False
69
Why are metals good conductors
The presence of delocalised electrons
70
Do metals have low or high mp and bp
High
71
Why do metals have high mp and bp
Metallic bonding is fairly strong
72
What does the strength of metallic bonds depend on
The number of outer electrons
73
What bonding generally exists between two non metals
Covalent bonds
74
How are covalent bonds formed
The merging of half filled electron shells
75
How are the atoms in a covalent bond held
By the electrostatic forces of attraction between positively charged nuclei and negatively charged shared electrons
76
What are covalent molecular elements?
Groups of atoms held together by covalent bonds inside the molecule yet weak intermolecular forces between the molecules
77
What are the covalent molecular structures in the first 20 elements
``` Hydrogen Nitrogen Oxygen Fluorine Chlorine Phosphorous (P4) Sulphur (S8) Carbon- fullerene ```
78
Are the mp and bp of covalent molecular structure low or high
Low
79
Why is the mp and bp of covalent molecular structure low
The weak LDF
80
What do covalent network structures consist of?
A giant lattice of covalent my bonded atoms
81
Name the elements in the first 20 elements in the periodic table which are covalent network elements
Boron Silicon Carbon- diamond or graphite
82
Do covalent network elements have high or low mp and bp
Very high
83
Why are the mp and bp of covalent networks very high
The covalent bonds which a very strong have to be broken at their melting and boiling points
84
What is graphite
Pure carbon
85
Why is graphite a good conductor of electricity
The layers of delocalised electrons
86
Where are the LDF in graphite
Between the layers
87
Describe the density, melting points and conduction of monatomic elements
Low density Low melting point No conduction
88
Describe the density, melting point and conduction of covalent molecular elements
Low density Low melting point No conduction
89
Describe the density, melting point and conduction of covalent network elements
Very high density Very high melting point Doesn't conduct except graphite
90
Describe the density, melting point and conduction of metallic elements
High density High melting points Does conduct
91
What is covalent radius
Half the distance between the nuclei of two bonded atoms
92
What happens to the covalent radius going down a group
Increases
93
Why does the covalent radius increase going down a group
Electron shells increase
94
Does the covalent radius increase or decrease going across a period
Decrease
95
Why does covalent radius decrease going across a period
Increasing nuclear charge due to increased number of protons
96
What is ionisation energy
The energy required to remove one mole of electrons from one mole of gaseous atoms of an element
97
What is the general equation representing the first ionisation energy of carbon
C(g)--->C+(g) + e-
98
What is the equation for the third ionisation energy of carbon
C2+(g) ---> C3+(g) + e-
99
Does the ionisation energy increase or decrease going down a group
Decrease
100
Why does the ionisation energy decrease going down the group
More electron shells so the electron if further from the nucleus Shielding effect
101
Does the ionisation energy increase or decrease going across the period
Increase
102
Why does the ionisation energy increase going across a period
Nuclear charge increases
103
What is electronegativity
Measure of attraction an atom has for the electrons bonded
104
What are the units for electronegativity
No units
105
Does the electronegativity increase or decrease going down a group
Decrease
106
Why does electronegativity decrease going down a group
Atomic size increases and so the shared electrons are further from the nucleus Greater shielding
107
Does the electronegativity increase or decrease going across a period
Increase
108
Why does electronegativity increase going across a period
Nuclear charge is increasing due to the increase in protons

Higher Chemistry (3 decks)

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