# C3

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• Created by: dkoning00
• Created on: 05-06-16 12:15
Define an Exothermic reaction
A reaction that gives out energy to the surroundings when new bonds are made, usually resulting in a rise in temperature
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Define an Endothermic reaction
A reaction that takes in energy from the surroundings in order to break existing bonds, usually resulting in a reduction in temperature
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Is thermal decomposition an Exothermic or Endothermic reaction? Give a reason
Endothermic - heat must be supplied for the compound to decompose (takes in energy)
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Will adding acid to alkali be exo- or endo- thermic?
Exothermic
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And dissolving Ammonium Nitrate in water?
Endothermic
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How could you measure the amount of energy given out/taken in by a reaction?
Measure the temperature of the reactants before an after (in solution)
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Energy must be supplied in order to...
Break existing chemical bonds
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Energy is released when...
Making new chemical bonds
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When does a chemical reaction become Exothermic?
When a greater amount of energy is released making new bonds than is taken in breaking existing ones
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When does a chemical reaction become Endothermic?
When a greater amount of energy is taken in breaking existing bonds than is released making new ones
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How could you compare the effectiveness of burning different fuels?
Calorimetric experiment - burn the fuels to heat an amount of water and measure the temperature change. By knowing the temp. change, mass of water and SHC you can work out how much energy is released per gram of each fuel
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What is the equation for energy transferred in Joules?
Energy transferred (J) = Mass of water (g) x SHC of water (4.2J/g dC) x Temp. change (dC)
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How do you calculate the energy given out by every gram in Joules per gram?
Energy given out per gram (J/g) = Energy released(J) / Mass of fuel burned(g)
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Describe the Calormetric method to gain the most accurate results
Reduce draughts and keep away from open windows; put fuel in burner or gas bottle and weigh; place specific amount of water in copper calorimeter; take initial temp. of water; light fuel; record highest temp. then reweigh burner & fuel
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How can this method be used to compare fuels?
Repeat the test for different fuels and compare the temperature change (energy released) to the amount of fuel burned - compare energy given out per gram
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How could you make sure this was a fair test?
Keep control variables the same (same amount of water, same equipment, conditions etc.) and repeat test several times for each fuel to increase reliability
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Give examples of slow, moderate and fast chemical reactions
Slow - rusting, chemical weathering. Moderate - metal reacting with dilute acid to produce gas bubbles. Fast - combustion, explosions.
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In what two ways can the rate of reaction from a reaction that produces gas be measured?
Measure the change in mass using electronic scales or measure the volume of gas released using a gas syringe. Both methods will require measurements to be taken at intervals to assess rate
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When will a reaction stop?
When at least one of the reactants runs out or the conditions don't allow the reaction to occur
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Using collision theory, explain what the rate of reaction depends on
The frequency of collisions between reactant particles (the more collisions there are per second, the faster the reaction) and the energy transferred during a collision (particles must collide with enough energy to make the collision successful).
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What is the mass of product directly proportional to?
The mass of the limiting reactant
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What is a limiting reactant?
The reactant that will be completely used up by the reaction causing it to cease
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What does a catalyst do?
Increases the number of successful collisions without the need for anymore energy input by providing a surface for the reaction to take place on but it is not used up
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What three other factors can increase the rate of reaction and how?
Increasing temp. - particles move faster with more energy so higher collision freq. and more successful collisions. Increasing concentration/pressure - particles become crowded so collide more often. Smaller solid particles - bigger surface area
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Why might industrial processes not use conditions that give the highest reaction rate?
Because creating the conditions (high temp. and pressure etc.) can be expensive so they may compromise to have a slower, cheaper reaction to reduce production costs
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From a rate of reaction graph how can you compare the rates of two reactions?
By comparing the gradient (steepness) of the graphs and at what points the reactions stop
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What is the Relative Atomic Mass (Ar)?
The total number of protons and neutrons in an atom's nucleus
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What is the Relative Formula Mass (Mr)?
The sum of relative atomic masses in a compound
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What is the Relative Formula Mass of Magnesium Chloride (MgCl2)
95
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Explain how mass is conserved in terms of reactions and equations
No atoms are destroyed or created in reactions so there will always be the same number of wtoms and the same mass. There must also be equal numbers of atoms on each side of a reaction's equation to show this
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Describe the mathematical process fro working out reacting masses
Write out the balanced symbol equation; work out the RFMs; Divide by the Mr of the reactant you're interested in to find out how much product 1g makes; times by however many grams are asked in the question to get the mass of product
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What is atom economy?
Tells you how much of the mass of reactants actually goes into the desired product and how much is wasted
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Give the atom economy equation
Atom economy = (Total Mr of desired products / Total Mr of all products) x 100
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What does a higher atom economy mean and why is it better?
Less of the reactants are being wasted which means the process is more sustainable, cheaper and better for the environment as less resources are wasted
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What is percentage yield?
A calculation that compares the predicted yield to the actual yield in order to tell you how successful the reaction was
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Give the percentage yield equation
Percentage yield = (Actual yield in grams / predicted yield in grams) x 100
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Why do industrial processes want a high percentage yield?
To reduce waste and costs by maximising useful resource output
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What are the four common ways percentage yield is reduced in an industrial process?
Liquids evapourating; not all the reactants making a product e.g. in reversible reactions; liquid lost in filtration and when being transferred e.g. some remaining in container
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What is batch production and what is it used for?
Production of small quantities of different drugs with the same equipment to order.
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Give advantages and disadvantages of batch production
It is flexible (can produce lots of different drugs) and start-up costs are relatively low because it is small scale. However, it is labour-intensive and quality control can be difficult
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What is continuous production and what is it used for?
Large scale production of one drug or chemical that doesn't stop
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Give advantages and disadvantages of continuous production
Because production never stops there is no time wasted resetting equipment, there is no need for human input and the quality is always very consistent. However, start-up costs for the whole factory are very large
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What three factors make producing and implementing a new drug so expensive and time consuming?
Research and development of compounds and chemicals in labs; Trialing and testing - all new drugs must be extensively tested to make sure they work and aren't harmful; Manufacturing - raw materials and equipment are expensive
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How are substances extracted from plants?
The plant is crushed, boiled and dissolved in a suitable solvent before the chemical can be separated by chromatography and extracted
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How can chromatography and boiling be used to assess purity?
Pure compounds will not be separated by chromatography and will have specific melting and boiling points whereas impure ones will separate and will have slightly different melting and boiling points
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What are allotropes?
Different structural forms of the same element
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Give three examples of allotropes of carbon
Diamond, Graphite and Fullerenes
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What are the properties of diamond and its uses?
Giant covalent structure with four covalent bonds per atom, lustrous, colourless, very hard and extremely high melting point due to strong bonds, doesn't conduct electricity asit has no free electrons. Used in cutting tools because of strength
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What are the properties of graphite and its uses?
Sheets of carbon atoms each with 3 covalent bonds, black, opaque, high melting point and can conduct electricity thanks to free electrons. Sheets can slide over each other making it a good lubricant and useful in pencils
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What are the properties of fullerenes and their uses?
Nanoparticles in the form of tubes or spheres of carbon atoms. Can be used for delivering drugs into the body and as a catalyst due to huge surface area
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What are giant molecular structures and what are their properties?
Structures made of lots of atoms of one element bonding together in a certain way (e.g. diamond or graphite). These are strong, have high melting points, don't dissolve in water and are usually non-conductive due to a lack of delocalised electrons
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## Other cards in this set

### Card 2

#### Front

Define an Endothermic reaction

#### Back

A reaction that takes in energy from the surroundings in order to break existing bonds, usually resulting in a reduction in temperature

### Card 3

#### Front

Is thermal decomposition an Exothermic or Endothermic reaction? Give a reason

### Card 4

#### Front

Will adding acid to alkali be exo- or endo- thermic?

### Card 5

#### Front

And dissolving Ammonium Nitrate in water?

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