C2 Flashcards
What are the four main things that effect rate of reaction?
Temperature, presence of a catalyst, surface area and concentration.
How does increased temperature effect rate of reaction?
Particles gain energy (become less dense) and therefore move more quickly and hit each other more often, thus speeding up the reaction. At a higher temperature, more particles would have ACTIVATION ENERGY.
How does presence of a catalyst affect rate of reaction?
Lowers the amount of energy needed for reaction. Has no affect on ACTIVATION ENERGY.
How does surface area affect rate of reaction?
Larger surface area for particles to hit speeds up reaction. Has no affect on ACTIVATION ENERGY.
How does increased concentration/pressure affect rate of reaction?
Particles hit each other more often, speeding up reaction. No affect on ACTIVATION ENERGY.
Exothermic
Heat is given out
Endothermic
Heat is taken in
Uses of endothermic reactions
Thermal decomposition. Eg. sports injury packs.
Uses of exothermic reactions
Burning fuels (combustion), neutralisation and oxidation reactions. Eg. hand warmers and self heating hot drink cans
Giant Covalent Structure
Non-metal atoms joined by covalent bonds and arranged in a giant lattice formation.
Characteristics of giant covalent structures
Very high melting points with variable conductivity.
Equilibrium
When the forwards and backwards reactions in a reversible reaction happen at the same time. Think going up the down escalator.
Haber Process
Industrial process used to make ammonia by turning nitrogen in the air into ammonia. It is a reversible reaction.
Steps of the Haber Process
- Nitrogen and Hydrogen purified
2. Passed over an iron catalyst at high temp (45 degrees) or put under high pressure (approx. 200 atmospheres)
Yield
Amount of product formed in a chemical reaction
Examples of Giant Covalent Structures
Diamond, Silica and Graphite
Combustion
Burning a substance
Electrolysis
Decomposition of an ionic compound using electricity
Two electrodes in electrolysis
Anode (positive) and Cathode (negative)
Electroplating
Covering one substance with a thing layer of another using electrolysis
Acids
Ionic compounds, broken down so hydrogen ions dissolve into the liquid. The more hydrogen ions, the stronger the acid.
Alkalis
A solution containing a BASE. This is an ionic compound that falls apart to form hydroxide ions.
Mole=
RFM x specified number of moles
Neutron (charge and mass)
Charge: 0 (neutral) Mass: 1
Electron (charge and mass)
Charge: - (negative) Mass: negligable
Proton (charge and mass)
Charge: + (positive) Mass: 1
Isotopes
Atoms of the same element with the same number of protons and electrons but different numbers of neutrons.
What is the electronic structure of sodium chloride? (sodium= Na+, chlorine=Cl-)
NaCl
What is the electronic structure of magnesium oxide? (magnesium= Mg^2+, oxygen= O^2-)
MgO
What is the electronic structure of calcium chloride? (calcium= Ca^2+, chlorine= Cl- and Cl-)
CaCl2
Empirical formula
Divide mass by RAM of each and and then simplify ratio
OIL RIG
Oxidisation Is Loss (gain of oxygen, loss of electrons at ANODE), Reduction Is Gain (gain of electrons at CATHODE)
Describe process of electrolysis:
- If you pass an electric current through any ionic substance if it’s molten or in a solution, it breaks down the elements it’s made of.
- Liquid called the electrolyte conducts the electricity.
- Electrolytes contain free ions, these conduct the electricity and complete the electrical circuit.
- Electrons are taken away from ions at the positive anode, and given away to ions at the cathode.
- As ions gain or lose electrons they become atoms or molecules and are released.
% Yield
total yield/ expected yield x 100
H+
Acid
OH-
Alkali
Useful products from Electrolysis of Sodium Chloride
- Many uses in the production of bleach and plastics (chlorine)
- Sodium hydroxide has many uses in the chemical industry eg. making soaps.
How does reactivity affect the products formed by electrolysis?
- At the cathode, if metal ions and H+ ions are present, the metal ions will stay in the solution if the metal is more reactive than hydrogen. (the more reactive an element, the keener it is the stay an ion)
- At the anode, if there are OH- ions and halide ions present, molecules of chlorine, iodine or bromine will be formed. If no halide is present. then oxygen will be formed.
Ionic Compound
Held together by strong electrostatic forces between oppositely charged ions.
Halogens
Group 7 of the periodic table, all react with alkali metals to form ionic compounds in which the halide ions have a single negative charge.
Substances with simple molecules
solids, liquids and gases with relatively low melting and boiling points due to weak intermolecular forces (not covalent bonds). Don not conduct electricity due to no overall electric charge.
Ionic Compounds (sodium chloride)
Regular structures (giant ionic lattices), strong electrostatic forces. High melting points and high boiling points, conduct electricity when melted or dissolved in water because ions are free to move and carry current.
Diamond
Each carbon atom forms FOUR covalent bonds, this makes diamond very hard.
Graphite
Each carbon atom bonds to three others, forming layers. Layers are free to slide over one another due to no covalent bonds between and WEAK INTERMOLECULAR FORCES. One electron from each carbon atom is delocalised, allow graphite to conduct heat and electricity.,
Fullerenes
Large covalent structures (hexagonal rings of carbon atoms) that can be used in medicine for drug delivery into the body, in lubricants, as catalysts, and in nanotubes for reinforcing materials, eg. tennis rackets.
Thermosoftening polymers
Consist of individual, tangled polymer chains. Polymer chains with CROSSLINKS between them so they do no melt when heated.
Collision Theory
Particles collide all the time, however they need to correct amount of activation energy in order to react. Rate of reaction can therefore be increased by increasing chance of particle collision or raising energy of particles.
Advantages and disadvantages of using a catalyst
Ad: Speeds up reaction- more product yield over less time
Disad: Have to keep reaction mixture very clean
Not all reactions use the same type of catalyst
Needs to be removed from product afterwards
5 ways of measuring the rate of reaction
Yield, amount of product used, change in mass, volume of gas given off, precipitation
Low density polyethene
Not crystalline. The material has a lower density than HDPE
the forces of attraction between polymer molecules are weakened
the material is less strong, and has a lower melting point, than HDPE
High density polyethene
Has a crystalline structure. The material has a higher density than LDPE
the forces of attraction between polymer molecules are strong
the material is stronger, and has a higher melting point, than LDPE.
Alloy
Made from two or more different metals. Different sized atoms distort layers and make it more difficult to slide over one another, making alloys harder than pure metals.
Shape memory alloy
Can retunr to their original shape after being deformed. Eg. Nitinol used in dental braces.
Properties of metals
Conduct heat and electricity because of delocalised electrons in their structures.
Nanoscience
Refers to structures that are 1-100nm in size, of the order of a few hundred atoms. May lead to the development of new technologies etc.
Mass number
total number of protons and neutrons in an atom
Benefits of using instrumental methods
accurate, sensitive and rapid which is particularly useful when the amount of a sample is very small
Instrumental methods
Detecting elements and compounds using machines
Gas chromotography
Example of an instrumental method. Allows the separation of a mixture of a substance. Time taken to pass through the column can help to identify substance. Output from gas chromotography can be linked to a mass spectrometer
Mass spectrometer
Used in gas chromatography. Number of peaks on the output of a gas chromatograph shows number of compounds present. POSITION OF PEAKS INDICATES RETENTION TIME. Molecular mass is given by molecular ion peak.
Why do some reactions not produce expected yield?
Reaction may not be able to go to completion because it is reversible.
Some product may be lost when it is separated from reaction mixture.
Some reactants may react in ways different from expected reaction.
Calculate rate of reaction
Rate of reaction= Amount of product used/ time
Soluble salts can be made from acids by reacting them with:
Metals- not all metals are suitable; some are not reactive enough where some are too reactive.
Insoluble bases- base is added to acid until no more will react and excess solid is filtered off
Alkalis- an indicator can be use to show when the acid and alkali have completely reacted to produce a salt solution
Insoluble salts
can be made by mixing mixing appropriate solutions of ions until a precipitate is formed
Precipitation
can be used to remove unwanted ions from solutions, eg treating water for drinking or in treating effluent
Aluminium
Manufactured by electrolysis of a molten mixture of aluminium oxide and cryolite. Forms at the negative electrode with oxygen at the positive. Positive electrode is made of carbon which reacts with oxygen to form CO2
Cryolite
The use of cryolite reduces some of the energy costs involved in extracting aluminium.
Making salts with acids and bases
When acids react with bases, a salt and water are made:
acid + metal oxide → salt + water
acid + metal hydroxide → salt + water
Making salts with metal and
Acids will react with reactive metals, such as magnesium and zinc, to make a salt and hydrogen:
acid + metal → salt + hydrogen
