C3 Flashcards
What type of reaction is rusting?
A slow reaction
What type of reactions are burning and an explosion?
Fast reactions
What does the rate of reaction measure?
The amount of product made in a specific time
For mass changes, how can the rate of reaction be measured?
g/s or g/min
For volume changes, how can the rate of reaction be measured?
cm³/s, or cm³/min
How can the rate of a reaction be increased?
By rasing the temperature, increasing the concentration (of liquids) or increasing the pressure (of gases)
When do chemical reactions stop?
When one of the reactants is used up
What does the amount of product formed in a reaction depend on?
The amount of reactant used
What is the ‘limiting reactant’ in a chemical reaction?
The one that is used up by the end of the reaction
When there are more reactants, what does this mean?
There are more reactant particles, so more product particles can be made.
What does the ‘limiting reactant’ in a chemical reaction determine?
The maximum amount of product that can be made.
How can you measure the rate of a reaction?
By monitoring the mass of a reaction mixture in a flask on a top pan balance, or measuring the volume of gas produced using a gas syringe
When do chemical reactions take place?
When particles collide with enough energy
What is the relationship between the collision of particles in a reaction and the speed of the reaction?
The more collisions there are between particles, the faster the reaction.
Why does a reaction at a low temperature cause a slow rate of reaction?
Because in a reaction at a low temperature, the particles move slowly. This means that there are less collisions between particles, and they collide with less energy, so there are less successful collisions.
Why does a reaction at a high temperature cause a fast rate of reaction?
Because in a reaction at a high temperature, the particles move fast, meaning that they collide more often and with higher energy. This results in more successful collisions.
What does increasing temperature do to particles in a chemical reaction?
It causes an increase in the particle’s kinetic energy, and so they move a lot faster.
With an increase in temperature, and therefore an increase in particle speed, what happens?
The number of collisions per second increases, and more frequent collisions between particles leads to a faster reaction
When particles collide at an increased temperature, they have more energy. What does this cause?
High energy collisions increase the chance of successful collisions: more energetic collisions lead to more successful collisions.
Why does a reaction where one or both reactants are in low concentrations cause a slow rate of reaction?
The particles will be spread out, and so they will collide less often, resulting in fewer successful collisions
Why does a reaction where one or both reactants are in high concentrations cause a fast rate of reaction?
Increasing concentration increases the number of particles in the same space, so they are all much more crowded together. The more crowded they are, the greater the chance of them colliding. This increases the number of collisions per second, and more frequent collisions leads to a faster reaction.
Why does a gas being under a low pressure cause a slow rate of reaction?
Because the particles are spread out, and so they will collide less often, resulting in fewer successful collisionsre
Why does a gas being under a high pressure cause a fast rate of reaction?
When the pressure is high, the particles are crowded more closely together. The particles collide more often, resulting in much more successful collisions (like high concentration of reactants in a solution).
What is the relationship between the surface area of a reactant and the speed of the reactant?
The larger the surface area of a reactant, the faster the reaction.
Do powdered solids or lumps of solid have a larger surface area compared to their volume, and why?
Powdered solids, because more sides are exposed.
Why do powdered solid reactants cause a faster rate of reaction?
Because there is a greater proportion of particles exposed, meaning that the particles have a greater chance of colliding with other reactant particles.
Why do workers in factories that handle powders have to be very careful?
Because just a spark can cause an explosion
What is an explosion?
A very fast reaction, in which huge volumes of gas are made
What is a catalyst?
A substance that changes the rate of a chemical reaction without being used up or changed at the end of the reaction.
What are catalysts often used for?
Speeding up the rate of a reaction
Why are catalysts very useful materials?
As only a small amount of catalyst is needed to speed up the reaction of large amounts of reactant
Every element in the periodic table has two numbers. What is the larger number?
The relative atomic mass (Ar)
What is the relative formula mass (Mr) of a compound?
The sum of the relative atomic masses of all the atoms present in the formula.
How do you work out the relative formula mass (Mr)?
Write down the formula of the compound, multiply the number of atoms of each element in the formula by its relative atomic mass (Ar), then add them all up
What is always the relationship between the total mass of the reactants and the total mass of the products?
The total mass of the reactants is always equal to the total mass of the products.
Why is the total mass of the reactants is always equal to the total mass of the products?
Because no atoms are created or destroyed in a chemical reaction
What is the mass of the product directly proportional to?
The mass of the reactant.
Sometimes, we are given the starting mass of only one reactant, and the mass of the final product. How do we work out the other reactant’s mass?
Minus the given reactant mass from the final product’s mass.
What is percentage yield?
A way of comparing the amount of product that is made (actual yield) to the product amount that was expected to be made (predicted yield)
What is the formula to calculate percentage yield?
percentage yield= (actual yield/predicted yield) x 100
What does 100% yield mean?
That no product has been lost: actual yield is the same as predicted yield
What does a 0% yield mean?
That do product has been made: actual yield is zero
Why is a high percentage yield desired in industrial processes?
Because it reduces waste and therefore cost.
How can products be lost in a reaction, resulting in percentage yield being less than expected yield?
Evaporation, filtration or during the transfer of liquids
What is atom economy?
A method of measuring the number of atoms that are wasted in a chemical reaction.
If all the atoms in the reactant are in the product, what is the atom economy?
100%
What is the equation to calculate atom economy?
relative formula mass (Mr) of desired products x 100/ Sum of relative formula mass (Mr) of all the products.
Why is a high atom economy wanted in an industrial process?
Because it reduces the amount of unwanted products and makes the process more sustainable.
What do EXOthermic reactions do?
Release energy to the surroundings and cause a temperature rise.
What do ENDOthermic reactions do?
Absorb energy from the surroundings and cause a temperature drop.
What can the energy given out by exothermic chemical reactions be used to do? Give two examples.
Heat things, produce electricity, make sound, and make light.
What can a calorimeter be used for?
Comparing the amounts of heat energy released by the combustion of different fuels.
What is the name used to describe an experiment when the amounts of heat energy released by the combustion of different fuels are compared?
A calorimetry experiment.
If you burn the same mass of each fuel in a calorimetry experiment, which fuel releases the most energy?
The one which produces the largest temperature rise
To do a fair test when conducting a calorimetry experiment, what do you need to do?
Use the same mass/volume of water, use the same calorimeter, have the burner and calorimeter the same distance apart, and burn the same mass of fuel.
To make your calorimetry reliable, what should you do?
Repeat the experiment and take an average of the temperature rise.
To help compare between fuels in a calorimetry experiment, what should you do, and how?
Calculate the energy released per gram of fuel by measuring the mass of the spirit burner before and after the experiment.
What should be used in a Calorimetry experiment?
A draught shield, a thermometer, a copper calorimeter, water, a spirit burner, fuel in the spirit burner, a stand for the calorimeter and a heat proof mat.
To compare fuels, what do you need to do?
Work out the amount of energy transferred per gram of fuel burned.
What is the formula used to calculate the amount of energy transferred by the fuel to the water in the calorimetry experiment?
energy transferred= mass of water heated (g) x Specific heat capacity (J/g/°C) x Change in temperature (°C)
What is the formula to work out the energy transferred per gram of fuel?
energy per gram = energy supplied (J) / Mass of fuel burned (g)
In a chemical reaction, which process is MAKING bonds?
EXOthermic
In a chemical reaction, which process is BREAKING bonds?
ENDOthermic
What are chemical reactions that release more energy when making bonds than breaking them?
EXOthermic reactions.
What can the energy given out by exothermic reactions be used to do?
Heat things, produce electricity, make sound and make light.
What can a calorimeter be used to do?
Compare the amounts of heat energy released by the combustions of different fuels. This is a calorimetry experiment.
How can you work out which fuel releases the most energy in a calorimetry experiment?
If the same mass of each fuel, the fuel that produces the largest temperature rise releases the most energy.
What is the formula used to work out the change in temperature in a calorimetry experiment?
temperature change= final temperature of water - start temperature of water
In a calorimetry experiment, what must be done to ensure that it is a fair test?
- Use the same mass (or volume) of water
- use the same calorimeter
- have the burner and calorimeter the same distance apart
- burn the same mass of fuel.
To make a calorimetry experiment reliable, what should be done?
Repeat the experiment and take an average (mean) of the temperature rise.
To help compare between fuels in a calorimetry experiment, what could be done?
You could calculate the energy released per gram of fuel by measuring the mass of the spirit burner before and after the experiment.
Define ‘batch process’, and say what can be made in this way.
Reactants are put into a reactor and the product is removed at the end of the reaction. Medicines and pharmaceutical drugs can be made this way.
What do batch processes do?
- make a product on demand and on a small scale
- can be used to make a variety of products
- are labour intensive; the reactor needs to be filled, emptied, and cleaned.
Describe what a continuous process is, and say what can be made in this way.
Reactants are continually fed into the reactor as the products are removed. The production of ammonia in the Haber process and sulfuric acid in the Contact process are made in this way.
What do continuous processes do?
- make a product on a large scale
- dedicate to just making one product
- operate all the time
- can run automatically
How can the materials used to make a medicine be extracted from plant materials?
- Crushing using a pestle and mortar
- Boiling and Dissolving using a suitable solvent
- Using chromatography to separate a concentrated solution
What do the costs for developing a new pharmaceutical drug include?
- the materials needed, which could be synthetic or natural
- research development and testing which can take many years
- labour; highly qualified staff are needed, and often lots of staff are needed. It can’t be automated as only small quantities are needed
- energy
- marketing
Why does it take so long for a new medicine to be put on the market?
Research and development can take a few years, and it can take even longer to carry out safety tests, including testing on human volunteers. There are very strict legal rules which a new medicine
What do diamond, graphite and buckminsterfullerene have in common?
They are all allotropes of carbon
What type of structure does diamond have?
rigid
What type of structure does graphite have?
layered
Why are diamonds used in jewellery?
Because diamond is colourless, clear, and lustrous.
Does diamond conduct electricity?
No
Is diamond soluble in water?
No
Why is diamond used in cutting tools?
Because it is very hard and has a very high melting point
What is diamond made of?
Carbon atoms bonded to four other carbon atoms by strong covalent bonds.
Why doesn’t diamond conduct electricity?
Because it doesn’t have any free electrons.
Why is diamond hard and why does it have a high melting point?
Because it has a large number of covalent bonds, which need a lot of energy to break.
Why is graphite used in pencil leads?
Because it’s black and slippery.
What is graphite made of?
Layers of carbon atoms that are bonded to three other carbon atoms by strong covalent bonds.
Why is Graphite used to make electrodes for electrolysis?
Because it conducts electricity and has a very high melting point.
Why is graphite used in lubricants?
Because it’s slippery.
Why is graphite slippery?
Because the layers are held together by weak intermolecular forces, allowing each layer to slide easily
Why does graphite conduct electricity?
Because it has free [delocalised] electrons.
Why does graphite have a high melting point?
Because it has many strong covalent bonds to break, which need a lot of energy to do so.
What is Buckminster fullerene?
60 carbon atoms arranged in a football-like sphere. It’s a black solid.
What does nanochemistry do?
It deals with materials on an atomic scale.
How are nanotubes made?
By joining fullerenes together
What are nanotubes used to do?
- Reinforce graphite tennis racquets because of their strength.
- Make conductors and semiconductors in circuits because of their electrical properties.
- Develop more efficient industrial catalysts.
How can fullerenes and nanotubes be used for medicinal purposes?
Their shape allows them to trap other substances, for example: a major new HIV treatment uses buckminster fullerene to deliver a material that disrupts the working of the HIV virus.
How can nanochemistry be used to develop more efficient industrial catalysts?
By attaching catalyst material to a nanotube, a massive surface area can be achieved, making the catalyst very efficient.
