- Created by: tylastallan
- Created on: 31-10-16 23:43
Properties Of Matter
Volume Of Gases
Standard Temperature and pressure (STP) is 0°C and 1 atmosphere (atm)
Volume Of Gas = number of moles x 22.4
V = n x22.4
n = v/22.4
Properties Of Gases
Gases all have similar properties
1. Low density compared with liquids or solids
2. They spread to fill the container in which they are placed
3. They exert pressure in all directions
4. They can diffuse easily and quickly
5. They are easily compressed
The Ideal Gas Law
For an Ideal Gas: PV= nRT
n= number of moles
R= the universal gas content
The value of R depends on the units used for pressure:
Dalton's Law Of Partial Pressure
The total pressure in a gas mixture is the sum of the partial pressures of each indiviual gas:
Ptotal= P1 + P2 + P3 ...
Diffusion is the tendency of gases to spread out e.g spaying deodrant
Effusion is when a gas escapes through a tiny hole in its container e.g a ballon
Graham's Law of effusion shows that the lighter gases effuse faster, than heavier gases
The pressure of a gas is due to the gas particles colliding with the walls of the container.
A barometer is a device used to measure atmoshperic pressure.
Pressure is measured in a number of units. The System International (SI) unit of pressure is the pascal (pa). Older units of pressure that are still used are millimetres of mercury (mm Hg) and atmospheres (atm).
1 atm = 760mmHg = 101.3 kPa
kPa = kilo pascals
= 1000 pascals
Increasing the pressure on a sample of gas will lead to a decrease in volume (keeping it the same temperature).
At a constant temperature:
Note: This only applies to an "ideal" gas, an ideal gas is one that follows the 5 assumptions of the kinetic molecular theory.
Kinetic Molecular Theory
1. Gases are made up of particles moving with rapid, constant random motion.
2. The higher the temperature, the faster the particles move. They have increased kinetic energy.
3. The forces of attraction and repulsion between the gas particles are pratically zero.
4. The particles are very far apart. The volume of the particles is very small compared with the volume that the gas occupies.
5. Particles collide with each other and the walls of the container exerting pressure. The collisions with each other are perfectly elastic. This means that no kinetic energy is lost when they collide with each other.
If all five basic assumptions are met, it is considered an "Ideal Gas"
Changing the temperature of a gas directly changes the volume occupied.
Pic On Right: Low temp = Small Volume
Pic On Left: High temp = Larger Volume
For a fixed amount of gas at a constant pressure:
Note: Temperature must be in Kelvin
Gay - Lussac's Law: Pressure and Temperature
If the volume of a gas is kept constant, as the temperature of the gas increases, the pressure increases.
At a constant volume:
Note: Temperature must be in Kelvin
The Combined Gas Law
The combined gas law combines Boyle's, Charles and Gay-Lussac's law's together.
The combined gas law allows you to do calculations when the amount (moles) of gas is constant:
Manipulating the Formula's
The combined gas law can be altered if pressure, volume or temperature is kept constant.
Pressure is constant - Charles Law
Volume is constant - Gay Lussac's Law
Temperature is constant - Boyle's Law
Ideal Vs. Real Gases
An Ideal Gas is a gas that obeys all the gas laws perfectly at a particular temperatureand pressure. No gas behaves ideally, however, at all temperatures and pressures. Real Gases show large departures from ideality, particulary at high pressures and low temperatures.
Enthalpy and Thermochemical Equations
Enthalpy (H) is the heat content of a system
The change in enthalpy ΔH is given by: Δ = delta/change in
ΔH = H(products) - H (reactants)
- Heat is released to the surroundings - ΔH is negative - It feels hot
- heat is absorbed from the surroundings - ΔH is positive - feel cold
A reversible reaction is one in which the conversion of reactants to products, and the conversion of products to reactants occur simultanelously
When the rates of the forward and reverse reactions are equal, a state of balance called chemical equilibrium has been reached.
Le Chatelier's Principle
Le Chatelier's Principle states that if a change is applied to a system at equilibrium, the system reacts in such a way as to counteract the change, in order to return to equilirbium.
- Increase in pressure favours side with fewer moles
- Decrease in pressure favours side with more moles
- When temperature is increased endothermic reaction is favoured
- When temperature is decreased exothermic reaction is favoured
- Rate Forward reaction = rate reverse reaction - No observable changes - Both directions of reaction are occuring
Heat on left of equation = endothermic
Heat on right of equation = exothermic
Changing Equilibrium Position
An acid is a substance which in solution produces hydrogen ions H+
Properties - sour to taste
- will dissolve in water
- they are neutralised by bases
Acetic acid CH3COOH
Carbonic Acid H2OCO3
Hydrochloric Acid HCl
In solids acids Ionise:
HCl --> H+ + Cl-
A base is a substance which in solution produces hydroxide ions OH-
Magnesium hydroxide Mg(OH2)
NaOH --> Na+ + OH-
Strength and Concentration
Strong Acids are completely disassociated (100%). If the acid is less then 100% disassociated it is termed a weak acid.
For strong acids in water show a one way arrow.
Weak acids are partially ionized or disassociated and therefore form few ions. A double arrow is used to indicate their dissolving in water.
Concentration is a ration of the amount of solute to the amount of solvent in a solution - usually measured in moles/litre (molarity)
Concentrated acids or bases have high molarity usually in excess of 6mol/L
Dilute acids have smaller molaritites usually less than 6mol/L
The acid Ka is the ratio of the ionised
1. Calculate the pH of a 0.05M solution of hydrochloric acid
(H+) = 0.05M
pH = -log(0.05)
pH = -(-1.3)
pH = 1.3
2. The pH of a solution is 6.35. What is the H+ ion concentration?
pH = -log (H+) (H+) = 10^-6.35
6.35 = -log (0.05) (H+) = 4.5 x 10^-7 M
-6.35 = log (H+)
Neutralization Reaction = acid and base react in aqueos solution to produce a salt and water
HCl + NaOH --> NaCl + H2O
acid base salt water