Lecture 1: Chemistry introduction

Question 1

Is there any structural formula for NaCl? Justify your answer.

Answer 1

No because it is an ionic compound. Not a covalent bond. (You cant just have a molecule, you have ions.)

Question 2

What is a molecular compound and an ionic compound?

Answer 2

Molecular Compounds are formed due to covalent bond between elements, while Ionic Compound is formed due to electrostatic force of attraction known as Ionic bond.

Question 3

What is the definition of a Mol?

Answer 3

1 mol is the number of atoms in exactly 12g of carbon-12. (6 x 10^23 atoms)

Question 4

Why are molar masses not presented as an integer in the periodic table?

Answer 4

The molar mass is a measure of the average molecular mass of all the molecules in a sample.

Question 5

Write the chemical, molecular and structural formula of ethanol (2 carbons, six hydrogens and one oxygen).

Answer 5

Question 6

How do you calculate Molarity?

Answer 6

Question 7

How many grams of NaCl in water is in each of the following three flasks? How many grams of water is in each of the three flasks?

Answer 7

A: There are 2 mols therefore their mass = 2*58.44g

B: There are 1 mol therefore its mass = 58.44g

C: 58.44g/2

Question 8

How do you prepare a solution of a soluble salt? Describe the steps and explain.

Answer 8

1. put the salt
2. put the water
3. dissolve everything
4. Then top it up to the top to the marker line.

Any idea why we do that?

because when you dissolve the salt the salt dissolves

Question 9

If you have 1l of a 5Molar solution of NaCl and need 300ml of a 2 Molar solution, how would you make the required solution?

Answer 9

volume = 1l

initial concentration = 5M

C_initialV_initial=C_finalV_final

Therefore 1000mlx5M=5000

= vol x 2M

5000/2 = Volume = 2500l

Therefore add 1500l of water and divide it by 1500/300ml

Question 10

Indicate what each arrow represents as a period property of the periodic table.

Answer 10

Ionization energy: the energy to take an electron out

Electron Affinity: The force to attraction electrons

Atomic radius: the size of atoms increases down the periodic table

The nucleus reduces as the proton and neutrons increase

Question 11

What does the octet rule say and how does this rule explain ionic and covalent bonds?

Answer 11

Octet rule: in covalent bond formation, atoms go as far as possible towards completing their octets by sharing electron pairs.

•Non-metallic elements form covalent bonds to one another by sharing pairs of electrons.

Question 12

What is a polar bond? Give an example.

Answer 12

A polar bond is a covalent bond between two atoms where the electrons forming the bond are unequally distributed. This causes the molecule to have a slight electrical dipole moment where one end is slightly positive and the other is slightly negative.h20

Question 13

Why do ethanol and acetone dissolve in water?

Answer 13

because ethanol and acetone are polar molecules with an arrangement such that the polar bonds are arranged in space so that the dipoles do not cancel out. They are able to attract their unequal dipoles to the dipoles in water molecules which are also polar.

Question 14

Enthalpy is defined as H = U + PV.

Why in biology and chemistry is enthalpy variation most of the times defined as ΔH = q, and what does q mean?

Answer 14

because you never have a variation in pressure as it is a closed system.

and u=q+w and workdone is usually 0 as well in biology and chemistry.

Question 15

What is a spontaneous process?

Answer 15

one that occurs without the addition of external energy.

Question 16

What is free energy and why does a decrease in it indicate a spontaneous process?

Answer 16

The free energy change is a measurement of the changes in the total entropy of a system and its surroundings at constant temperature and pressure.

Negative free energy, at constant temperature and pressure, indicates that it will react spontaneously.

Question 17

What is Gibb’s free energy?

Answer 17

ΔG =ΔH -TΔStot

Question 18

What does the second law of thermodynamics state?

Answer 18

that the entropy of the universe always increases for a spontaneous process.

Question 19

When you have a negative free energy does it mean that you will always have a reaction happening in your experiment?

Answer 19

-if it is positive it will not happen. decomposition will happen spontaneously.

if it is negative it will. It is spontaneous. It should happen.

Question 20

How would you construct a phase diagram of water? What would be the mandatory steps that you should pay more attention to, to be sure the phase diagram is correct?

Answer 20

Critical point

Triple point - where all three phases to exist.

3 phases: solid, liquid and gas.

Sublimation curve(solid-gas), fusion curve(solid-liquid) and vapor pressure curve (liquid-gas)

Question 21

In the phase diagram below, where can you find 5 phases in equilibrium?

Answer 21

the point between j k l h and i.

Question 22

On the phase diagram below, choose a point where you have liquid in equilibrium with the gas phase, and write down the composition of each phase.

Answer 22

%liquid = D2/D1+D2

%vapor=D1/D1+D2

Question 23

What is the molecular formula?

What is the empirical formula?

Answer 23

The molecular formula is the actual number of elements per molecule.

C₆H₁₂0₆

The Empirical formula is the proportion of elements per molecule.

CH₂O

Question 24

What is the first law of thermodynamics?

Answer 24

The internal energy of an isolated system is constant.

ΔU = q + w

q = heat

w = work

Question 25

The entropy equation?

Answer 25

The entropy of an isolated system increases in the course of any spontaneous change.

S= klnW

W: number of ways that the atoms or molecules in the sample can be arranged and yet still give rise to the same total energy.