4. Physical Chemistry Flashcards
describe experiments to prepare soluble salts from acids
Dilute sulphuric acid is added to an excess of magnesium.
Mg + H2SO4 > MgSO4 + H2
The left over magnesium is filtered off and the mixture boiled down slowly to concentrate.
When it is cooled, crystals will form, these can be blotted dry with a piece of paper.
This can be done with other metals and acids:
Nitric, sulphuric and hydrochloric acids make soluble salts with most metals.
ammonium, potassium and sodium make soluble salts with acids
describe experiments to prepare insoluble salts using precipitation reactions
Silver nitrate and sodium chloride are added together, the product, silver chloride is made, this salt is insoluable and so will form a white precipitate in the solution.
AgNO3 + NaCl > AgCl + NaNO3
predict the effects of changing the pressure and temperature on the equilibrium position in reversible reactions.
If you move the equilibrium, you change the rate of reaction.
If the equilibrium moves to the right, you have more products. (the reactants are reacting faster)
If the equilibrium moves to the left, you have more reactants. (the products are reacting faster)
If you increase the pressure: the equilibrium will move to the side with least molecules.
If you decrease the pressure: the equilibrium will move to the side with the most molecules.
If you increase the temperature, there will be more products that are produced by an endothermic reaction.
This is because the reaction is trying to use up the extra heat, and it does so by putting the energy into making bonds.
Define ‘dynamic equilibrium’
Dynamic equilibrium is when a reversible reaction is happening both ways at the same time, at the same rate.
describe reversible reactions such as the dehydration of hydrated copper(II) sulfate and the effect of heat on ammonium chloride
If you add water to copper sulphate you can make hydrated copper sulphate.
If you remover the water from hydrated copper sulphate you can make copper sulphate.
When heated, ammonium chloride splits into to hydrogen chloride and ammonia.
Hydrogen chloride and ammonia can be reacted to make ammonium chloride.
What is the role of a catalyst?
A catalyst provides an alternative route for the reaction to start, this route requires less activation energy to start the reaction.
What are the effects of changes in…
surface area of a solid
concentration of solutions
pressure of gases
temperature
…on the rate of a reaction in terms of particle collision theory
Collision theory says that to react particles must:
Collide with enough energy to react
Collide in the right orientation to react (the more frequent the collisions, the more likely this is)
Surface area:
Particles collide more frequently if there is more surface area, as there is more contact between the reactants. Faster rate of reaction.
Concentration/ pressure:
There is more chance of particles colliding at a higher concentration/pressure, so they react more often. Faster rate of reaction.
Temperature:
Particles move about more and will collide more frequently the higher the temperature; react more often. Increases the rate of reaction.
Catalyst:
Provides an alternative pathway for the reaction to start which requires a lower activation energy.
describe experiments to investigate the effects of changes in surface area of a solid, concentration of solutions, temperature and the use of a catalyst on the rate of a reaction
Surface area:
Put a set mass of magnesium in hydrochloric acid
Time the reaction
Change the from of magnesium keeping the mass the same (powder, wire, strips)
The more surface area (the smaller the pieces of magnesium) the faster the reaction
Concentration:
Put a set mass of marble chips into dilute hydrochloric acid
Time the reaction
Change the ratio of water to hydrochloric acid
The more concentrated the hydrochloric acid (the lower the ratio of water) the faster the reaction
Temperature:
Put a set mass of magnesium powder into a set mass of hydrochloric acid
time the reaction
Carry out this reaction at different temperatures
The higher the temperature the faster the rate of reaction
Catalyst:
If you have hydrogen peroxide it will not decompose
If you put it with manganese dioxide it will decompose into water and oxygen
The manganese dioxide will be unaltered by the reaction
The more of the catalyst the faster the reaction
use average bond energies to calculate the enthalpy change during a simple chemical reaction.
To work out the enthalpy change you do:
the sum of bond energies in the reactants - the sum of bond energies in the products
Given average bond energies, you can easily work out the sum of bond energies. For example, if we are told that C-H = 413 O=O= 498 C=O= 746 H-O=464
Work out the enthalpy change for this reaction: CH4 + 2O2 > CO2 + 2H2O
(4 x C-H) + (2 x O=O) - (2x C=O) + (4 x H-O)
Then we substitute in:
(4 x 413) + (2 x 498) - (2 x 746) + (4 x 464) = 2648KJ - 3348KJ = 700KJ enthalpy change
understand the use of ΔH to represent enthalpy change for exothermic and endothermic reactions
ΔH is the symbol that represents the amount of energy lost or gained in a reaction.
+ΔH is endothermic (because it gains heat)
-ΔH is exothermic (because it looses heat)
describe simple calorimetry experiments for reactions such as combustion, displacement, dissolving and neutralisation in which heat energy changes can be calculated from measured temperature changes
Measure the temperature at the beginning of the experiment, measure the temperature at the end. How ever much heat has gone up or down is the calorimetry of the reaction.
For example if you have a beaker of water and take its temperature, then burn a piece of bread under it, the change in temperature is the calories (energy) of the bread.
What are the general rules for predicting the solubility of salts in water?
i) all common sodium, potassium and ammonium salts are soluble
ii) all nitrates are soluble
iii) common chlorides are soluble, except silver chloride
iv) common sulfates are soluble, except those of barium and calcium
v) common carbonates are insoluble, except those of sodium, potassium and ammonium
predict the products of reactions between dilute hydrochloric, nitric and sulfuric acids; and metals, metal oxides and metal carbonates
Metals:
Hydrochloric acid + metal > metal chloride salt + hydrogen
Nitric acid + metal > You don’t need to know
Sulphuric acid + metal > metal sulphate + hydrogen
Metal oxides:
Hydrochloric acid + metal oxide > metal chloride salt + water
Nitric acid + metal oxide > metal nitrate salt + water
Sulphuric acid + metal oxide > metal sulphate + water
Metal carbonates:
Hydrochloric acid + metal carbonate > metal chloride salt + water + carbon dioxide
Nitric acid + metal carbonate > metal nitrate salt + water + carbon dioxide
Sulphuric acid + metal carbonate > metal sulphate + water + carbon dioxide
What are the sources of acids?
What are the sources of alkalis?
Essentially if something is acidic it contains positive hydrogen ions (H+), if something is alkaline it contains negative hydroxide ions (OH¯)
describe the use of the indicators litmus, phenolphthalein and methyl orange to distinguish between acidic and alkaline solutions
Red litmus paper turns blue in the presence of alkali.
Blue litmus paper turns red in the presence of acid.
Phenolphthalein goes pink in alkalis.
Methyl orange is yellow for alkali, red for acid.
