Unit 1

Question 1

Why is controlling rate of reaction important in industrial processes

Answer 1

If they are too low a manufacturing process will not be economically viable, too high and there is a risk of thermal explosion.

Question 2

What is relative rate?

Answer 2

the reciprocal of the time taken for the reaction.

Question 3

What is enthalpy change?

Answer 3

energy difference between the products and the reactants.

Question 4

What is the activation energy?

Answer 4

minimum energy required by colliding particles to form an activated complex.

Question 5

What is an activated complex?

Answer 5

unstable arrangement of atoms formed at the maximum of the potential energy barrier, during a reaction.

Question 6

How can the effect of temperature on rate of reaction be explained?

Answer 6

an increase in the number of particles with energy greater than the activation energy.

Question 7

Different types of bonding and structures and examples?

Answer 7

• metallic (Li, Be, Na, Mg, Al, K, Ca)
• covalent molecular (H2, N2, O2, F2, Cl2, P4, S8 and fullerenes (eg C60))
• covalent network (B, C (diamond, graphite), Si)
• monatomic (noble gases)

Question 8

What is electronegativity

Answer 8

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

Question 9

What is a covalent bond?

Answer 9

• In a covalent bond, atoms share pairs of electrons.
• The covalent bond is a result of two positive nuclei being held together by their common attraction for the shared pair of electrons.

Question 10

When are polar covalent bonds formed?

Answer 10

• Polar covalent bonds are formed when the attraction of the atoms for the pair of bonding electrons is different.
• Delta positive (δ+) and delta negative (δ-) notation can be used to indicate the partial charges on atoms, which give rise to a dipole (eg H δ+̶ Clδ-).

Question 11

Where do ionic bonding and purely covalent bonding lie on the continuum?

Answer 11

Pure covalent bonding and ionic bonding can be considered as being at opposite ends of a bonding continuum with polar covalent bonding lying between these two extremes.

Question 12

What happens if the difference in electronegativities are large

Answer 12

• If the difference is large then the movement of bonding electrons from the element of lower electronegativity to the element of higher electronegativity is complete resulting in the formation of ions.
• Compounds formed between metals and non-metals are often, but not always ionic.

Question 13

What are London Dispersion forces

Answer 13

• London dispersion forces are forces of attraction that can operate between all atoms and molecules.
• These forces are much weaker than all other types of bonding.
• They are formed as a result of electrostatic attraction between temporary dipoles and induced dipoles caused by movement of electrons in atoms and molecules.

Question 14

why is a molecule polar?

Answer 14

The spatial arrangement of polar covalent bonds can result in a molecule being polar.

Question 15

Is PD-PD stronger or LDF?

Answer 15

Permanent dipole-permanent dipole interactions are stronger than London dispersion forces for molecules with similar numbers of electrons.

Question 16

What is hydrogen bonding?

Answer 16

• Bonds consisting of a hydrogen atom bonded to an atom of a strongly electronegative element such as fluorine, oxygen or nitrogen are highly polar.
• Hydrogen bonds are electrostatic forces of attraction between molecules which contain these highly polar bonds.
• A hydrogen bond is stronger than other forms of permanent dipole-permanent dipole interaction but weaker than a covalent bond.

Question 17

What does hydrogen bonding in ice result in?

Answer 17

Hydrogen bonding between molecules in ice results in an expanded structure which causes the density of ice to be less than that of water at low temperatures.