Chemistry 6 Flashcards
In what state does pressure affect rate of reaction ?
Gases
What four things affect rate of reaction ?
Temperature
Concentration
Catalyst
Surface area of solids
How can you find the rate of reaction ?
Amount of reactant used or amount of product formed divided by time
Give three ways rate of reaction can be measured ?
Precipitation
Change in mass
Volume of gas given off
How do you measure rate of reaction with precipitation ?
Place a cross, or mark, below the solution and time how long it takes before the mark is no longer visible
What do you look for when measuring a change in mass ? How do you find this ?
You are looking for a change in the mass, the quicker the change the faster the rate of reaction. To find this you place the solution on weighing scales and let the reaction take place
What piece of equipment measures the volume of gas given off ?
A gas syringe
How is the volume of gas given off in a reaction measured ?
A gas syringe measures the gas given off by collecting it as it leaves the beaker. The more gas given off the faster the rate of reaction
What is an example of an experiment that measures volume given off ?
The reaction of hydrochloride acid and marble chips
Name a reaction that is good for measuring a change in mass
Magnesium metal with dilute hydrochloric acid
What does the decomposition of hydrogen peroxide show ?
The effects of different catalysts on rate of reaction
What catalyst speeds up the decomposition of hydrogen ?
Manganese (IV) oxide catalyst
What is collision theory ?
More collisions between particles increases the rate of reaction.
How does temperature increase rate of reaction in regards to collisions ?
When the temperature increase the particles gain energy and move quicker. If they move quicker they will collide more often
How does higher concentration increase collisions ?
If there is a higher concentration there are more particles in the same amount of space. Therefore they are more likely to collide as the space becomes confined
Why does a smaller surface area increase the rate of reaction ?
The particles, when smaller, have a larger area to work on so they can collide with more things and more frequently
What is a catalyst ?
A catalyst is a substance which speeds up a reaction, without being changed or used up in the reaction
How does using a catalyst reduce cost in industrial reactions ?
- By increasing rate of reaction the plant doesn’t need to operate for so long because it happens quicker
- Works at a lower temperature, reducing energy costs
What are the disadvantages of using catalysts ?
- They are expensive
* they can be ‘poisoned’ by impurities and stop working
What is an exothermic reaction ?
A reaction which transfers energy to the surroundings, usually in the form of heat and shown by a rise in temperature
What is the best example of an exothermic reaction ?
Combustion - it gives out a lot of heat through burning
What is an endothermic reaction ?
A reaction which takes i energy from the surroundings, usually in the form of heat and shown by a fall in temperature
What is a good example of an endothermic reaction ?
Thermal decomposition
If a reversible reaction is endothermic one way, what will it be the other way ?
Exothermic, the energy absorbed one way is equal to the energy released the other
What number is neutral on the pH scale ?
7
What numbers are acids on the pH scale ?
0-6
What numbers are alkalis on the pH scale ?
8-14
What is an indicator ?
A dye that changes colour depending on whether it’s above or below a certain pH
What are substance with a pH of greater than 7 also known as ?
A Base
In what way is an alkali different to a base ?
An alkali is a base that dissolves in water
Acid + base —> ?
Salt + water, this is called neutralisation
What does aq stand for and what does it mean ?
Aqueous- dissolved in water
Metals + acid —-> ?
Salts + hydrogen
What happens when sodium is reacted with acid ? And why ?
They react explosively because sodium is a very reactive metal
Why does copper not react at all with dilute acids ?
It is less reactive than hydrogen
What type of salt does hydrochloric acid produce ?
Chloride salts
Sulphate salts come from what acid ?
Sulphuric acid
What do metals less reactive than hydrogen not do ?
React with acid
What are metal oxides and metal hydroxides ? And why ?
Bases - because they have a pH of over 7. Some dissolve in water - these are alkalis
How can ammonia be converted into fertiliser ?
Neutralisation - ammonia dissolves in water to form an alkaline solution. This is reacted with nitric acid to form a salt (ammonium nitrate) - the fertiliser
Why type of salts do chlorides, sulfates and nitrates mostly make ?
Soluble salts (in water)
Insoluble salts in water are made by what ?
Most oxides an hydroxides, some break the rule
What does electrolysis mean ?
Splitting up with electricity
How does electrolysis work ?
An electric current is passed through an ionic substance that’s molten or in solution, it breaks down into the elements it’s made of
What is the electrolyte ?
A liquid that conducts the electricity for electrolysis
Oxidation is …
Loss
Reduction is …
Gain
Do oxidation and reduction have to involve oxygen ?
No, it is used in electrolysis with the loss or gain of electrons
True or false - only oxidation is involved in electrolysis
False - electrolysis always invokes oxidation and reduction because one electrode loses electrons and the other gains electrons
Lead bromide is a salt, what does it have to be to conduct electricity ?
Molten
Describe the electrolysis of lead bromide
The molten lead bromide acts as the electrolyte, lead is produced at the +ve electrode and bromide at the -ve
What happens at the negative electrode if the metal ions and H+ ions are present ?
If the metal is more reactive than hydrogen it will stay in solution because more reactive elements want to stay as ions. So hydrogen is produced
What happens at the positive electrode if OH- and halides (Cl-, Br-, I-) are present ?
Molecules of either chlorine, Bromine or Iodine will be formed. I no halides are present then oxygen will be formed
What is common salt ?
Sodium chloride
What three things are produced when common salt is electrolysed ?
Hydrogen
Chlorine
Sodium Hydroxide
What is produced at the negative electrode when sodium chloride is electrolysed ?
Hydrogen
What is found at the positive electrode when common salt is electrolysed ?
Chlorine
Where is sodium hydroxide found once electrolysis of common salt is complete ?
Left in the solution
What is bauxite ?
The main ore of aluminium, aluminium oxide
How is cryolite used in the purification of aluminium in bauxite ?
Bauxite is dissolved in molten cryolite. Bauxite has a very high melting point, so it would be very expensive to electrolyte, cryolite is lower which reduces the costs
What is electroplating ?
Using electrolysis to coat the surface of one metal with another metal
What is at the negative electrode when electroplating ?
The metal object you wish to plate
What is at the positive electrode when electroplating ?
The pure metal you want the object to be plated with
What does the electrolyte need to contain in electroplating ?
It needs to contain the ions of the plating metal
How can electroplating be used ?
Decoration - to cover cheaper metals in more expensive metals
Conduction - copper can coat electronic circuits to conduct electricity