Chemistry- Additional Flashcards
Describe how temperature and the collision theory work?
As temperature increases the particles have more energy therefore they move quicker and collide more often therefore they are more likely to overcome the activation energy as the collisions have more energy, this increases the rate of reaction
Describe how concentration and the collision theory work?
If it is more concentrated there are more reactant particles which make the collision more likely - low pressure
If there is more pressure the particles are more squashed so there is more frequent collisions, this increases the rate of reaction
describe how surface area and the collision theory work?
The smaller the pieces the larger the surface area therefore the particles have more area to work on so there are more frequent collisions, this increases the rate of reaction
How does a catalyst and the collision theory work?
A catalyst speeds up the rate of reaction without being changed or used up in the reaction, it also lowers the activation energy so more collisions are successful
Why are catalysts good in industry?
- save money
It increases the rate of reaction so it doesn’t have to operate for as long as it would without a catalyst - lowers temperature
Reduces the amount of energy needed so saves money and is good for sustainable development - expensive
But it never gets used up in the reaction - can be poisoned by impurities so the mixture has to be very clean
- they only work for one kind of reaction
What is an exothermic reaction?
One which transfers energy to the surroundings usually in the form of heat and is shown as a rise in temperature
Give examples of an exothermic reaction?
Combustion
Neutralisation
Oxidation
How does a un reusable hand warmer work?
The iron turns into hydrated iron (II) oxide, sodium chloride is used as a catalyst
What are the advantages and disadvantages of a un reusable hand warmer?
- only used once
- last for hours
How does a re usable hand warmer work?
A small metal disc in the plastic pack is used to start the exothermic reaction, a few metal particles are scrapped of which starts the crystallisation and spreads throughout the pack giving off energy, can be dissolved in heat
What are the advantages and disadvantages of an reusable hand warmer?
- reversible
- last for 30 minutes
What is an endothermic reaction?
One which takes in energy from the surroundings usually in the form of heat and is shown by a fall in temperature
Give an example of an endothermic reaction?
Thermal decomposition
How do cold packs work?
The ammonium nitrate dissolves in the water and takes in energy from the surroundings making the pack cold
How do you get blue crystals?
Heat blue hydrated copper(II) sulfate crystals and it evaporates the water off leaving a white hydras copper sulfate powder, this is endothermic
Add a couple of drops of water to the White powder and you get blue crystals, this is exothermic
What is the collision theory?
Particles must collide with enough energy to overcome the activation energy, particles with less energy bounce off each other
What is a pH?
A measure of how acidic or alkaline a solution is
Where is acid on the pH scale?
0-6
What is an indicator?
A dye that changes colour depending on wether the substance is above or below a certain pH
What is a universal indicator?
A combination of dyes that turn colour as the pH changes, it is the best for estimating the pH of a solution
What do acids form in water?
Hydrogen ions
What is a base?
An substance with a pH greater than 7
What is an alkali?
An alkali is a base that dissolves in water to form hydroxide ions
What is neutralisation?
A reaction between acids and bases
What do you get when you react an acid with a base?
Acid+base>salt+water
What do you get when you react an acid with metal?
Acid+metal>salt+hydrogen
If the metal is more reactive what will happen?
The more reactive the metal the faster the reaction will go, or they will react explosively
Why does copper not react with dilute acids?
Because its less reactive than hydrogen
What is the speed of reaction indicated by?
The rate at which hydrogen bubbles are given off
How do you work out that hydrogen is produced?
Squeaky pop test
What is the equation for hydrochloric acid?
HCL
What is the equation for sulphuric acid?
H2SO4
What is the equation for nitric acid?
HNO3
What happens when you mix a metal oxide with acid?
Acid+metal oxide>salt+water
What happens when you mix a metal hydroxide and a acid?
Acid+metal hydroxide>salt+water
What is ammonia useful for?
Ammonia can be neutralised by nitric acid to produce a fertiliser, the ammonia dissolves in water to make an alkaline solution, no water is produced and plants need it to make protein
How do you make a salt with a base or insoluble base? (The method of crystallisation)
Add metal oxide and metal hydroxide to the acid
The solid will dissolve in the acid as it reacts
When the acid has been neutralised the excess solid will just sink to the bottom
Then filter the excess metal, metal oxide and metal hydroxide to get the salt solution
Or evaporate the water this makes the solution more concentrated to get pure solid crystals of the salt this is called crystallisation
How do you make salts using an alkali?
- Cant use the method above with alkalis as you wont be able to tell when the reaction has finished
Add an indicator to show when the reaction has finished
Then repeat adding the exact volume of alkali and acid so the salt is not contaminated by the indicator
Then evaporate the water to crystallise the salts as usual
How do you make insoluble salts?
Combine 2 salts that contain different soluble salts
Mix the two ions you need and the salt will precipitate out
Filter it from the solution, wash it than dry it again
What is electrolysis?
Splitting up using electricty
What does electrolysis require ?
It requires the electrolyte, this is a liquid to conduct electricity
How do electrolytes conduct electricity?
Electrolytes contain free ions they are usually molten or dissolve ionic substances, the free ions conduct the electricity and make the whole thing work
OIL RIG
Oxidation Is Loss Reduction Is Gain
How does the electrolysis of sodium chloride solution work?
At the negative electrode 2 hydrogen ions accept 2 electrons and become a hydrogen molecule
At the positive electrode 2 cl- ions lose electrons and become one chlorine molecule
Sodium ions stay in solution as they are more reactive than hydrogen, and hydroxide ions from water are
Left behind, sodium hydroxide is left in the solution
What happens if there is more than 2 free ions?
There will be some hydrogen and hydroxide ions
What happens at the negative electrode?
At the negative electrode if metal ions and hydrogen ions are present the metal ions will stay in the solution, if the metal is more reactive than the hydrogen then the more reactive element will want to stay as an ion
What happens at the positive electrode?
If OH- ions and halide ions are present than molecules of chlorine and bromine and iodine will be formed, if there is no halide then oxygen will be formed
What do half equations do?
Show the reaction at the electrodes
What are the useful products of sodium chloride?
Chlorine = bleach and plastics
Sodium hydroxide = soap
Hydrogen = margarine (hydrogen+ vegetable oils)
What is the main ore of aluminium?
Bauxite
What is left after you purify and mine aluminium?
A white powder of aluminium oxide is formed, this has to be extracted by electrolysis
How do you do electrolysis of aluminium oxide?
Aluminium oxide has a high melting point do melting it would be 2 expensive
Therefore the aluminium has to be dissolved in molten cryolite
This decreases the melting point and makes it cheaper and easies
The electrolytes are made of carbon graphite because it is a good conductor of electricity
The aluminium forms at the negative electrode and the oxygen forms at the positive electrode
At the positive electrode the oxygen reacts with the carbon to form carbon dioxide therefore it has to be replaced every so often
What is electroplating?
Uses electrolysis to coat the surface of one metal with another
How does electroplating work?
The negative electrode is the metal object you want to plate and the positive electrode is the pure metal you want it to be plated with
The electrolyte has to contain ions of the plating metal
What does electroplating do to the object?
Attractive Cheaper Conducts electricity Protect the object Hardness of surface makes it resistant to scratching
