Lecture 2 Flashcards
What are Hydrogen bonds?
Intermolecular, attractive forces, which are a type of polar bond
Where do H bonds occur?
Between Hydrogen and F, O and N.
These are very electronegative and suck electrons towards each other
What is a polar covalent bond?
An uneven sharing of electrons (more than covalent, but less than ionic)
Are H bonds stronger than most other van der waal forces?
Yes
What is the primary intermolecular force within liquid water?
Hydrogen bonds
Why does ice occupy more space than water?
As the temperature decreases below 4 degrees, It will strengthen the Hydrogen bonds between the water molecules so that they are more rigid.
As a result, they form a more open, crystallised structure with large spaces in between the bonds.
Thus ice occupies more space than water, hence a beer bottle in the freezer will pop
What factor affects the balance of forces of a molecule?
The distance between molecules
What is a net energy curve?
A curve of attraction and repulsive forces vs. distance
What does a net energy graph tell us?
as distance decreases, net energy becomes an attractive force, but there is still something which prevents the molecules from collapsing into each other
There is a distance where attraction forces equal repulsive forces.
How does temperature change the net energy graph?
As we heat ice and it melts, the shape of the curve will change.
Although the curves look different at different temperatures the shape/pattern remains the same.
i.e. molecules cant come too close together or repulsive forces will take over
What is the behaviour of gases?
They move in random directions and try to fill the space.
What causes the pressure of a gas?
gaseous molecules pushing the edge of the container
Why doesnt a balloon collapse when filled with air?
the molecules in the air are bouncing against the walls of the baloon to hold i out
What keeps the balloon in shape?
The balance between the gas molecules bouncing against the wall of the baloon, and the natural elastic recoil of the baloon
How does temperature affect the way gaseous molecules move?
If you increase temperature, gas molecules have more energy to move around. likewise if you decrease temperature, molecules move slowly.
So if you freeze a balloon it shrinks because molecules do not bounce against the walls as much due to lower temperature.
likewise if you throw a canister into fire, temperature will increase, causing molecules to move faster, resulting in increased pressure which can cause the canister to explode
What is the number of collisions of gaseous molecules equal to?
The number of particles. the more gaseous molecules there are inside a balloon the more frequently they will hit the walls, hence the higher the pressure
What is pressure proportional to?
temperature.
at higher temperatures, things move faster and hit the walls of the container more
What is the number of collisions inversely proportional to?
the volume.
if we took all the gas molecules and put it in our hands there would be more collisions as they occupy a smaller space. however if we opened up the volume to the whole room they would have to travel further to hit a wall so the number of collisions decrease
What does a bigger volume therefore mean?
a reduced pressure
What does the ideal gas law tell us?
PV = nRT
where R is the universal gas constant
tells us that equal volumes of gas at the same temperature or pressure have an equal number of molecules regardless of the type of gas it is
What does an ideal gas mean?
there are no interactive forces between the molecules.
with a gas, there is a huge distance between molecules. They are so far apart we can assme no real attractive or repulsive forces
Gases behave differently to other states
what is liquefaction?
The conversion of a solid or a gas to a liquid
How is liquefaction achieved from a gas?
A temperature decreases, Ek is removed.
Gas molecules move more slowly
Pressure decreases so molecules will move closer to each other
eventually molecules are so close, attractive forces predominate and causes gaseous particles to collapse into the liquid state
What is the critical temperature?
the last moment where you can turn a gas back into a liquid?
Above this temperature, no matter how much pressure you apply, you cannot turn it back into a liquid
How can critical temperature be an indication of the intermolecular forces between the molecules?
Anywhere over 5.2K (kelvin) we cannot get liquid helium however water can be heated to high temperatures and still turn into a liquid. This shows that water has strong intermolecular forces including H bonding so can still be converted into a liquid whereas at high temperatures it is harder to get He to form a liquid
What is an aerosol?
a liquid or solid drug dissolved in a volatile propellant (usually liquid under the pressured confines of a can) e.g. shaving gell, deodorant
How do aerosols work?
When you press down on the buttton it opens a valve and a small amount of the pressurised liquid, including the drug/active ingredient etc escapes
This opens up as a gas as soon as it reaches atmospheric pressure
Why were traditional propellants like CFC and NFC replaced?
Replaced by FC’s and others as they were bad for the ozone layer
Why is the aerosol a liquid inside the canister?
The pressure inside the canister is higher than atmospheric pressure so molecules are forced closer.
This causes attractive forces to predominate and so the aerosol is a liquid.
As it moves into atmospheric pressure, molecules can move away from each other and are no longer under the effect of attractive forces, so move apart to form a gas
What is vapour pressure?
the pressure exerted by a vapor in thermodynamic equilibrium with its condensed phases (solid or liquid) at a given temperature in a closed system
aka the tendency of the particles of a liquid to escape into the vapour phase.
High vapour pressue = high volatility of liquid
