AQA Chem2

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What is an Enthalpy change?
The name given to the amount of heat evolved/absberd carried out at a constant pressure/temperaure.
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How do you calculate the enthalpy chage?
Enthalpy of reactants-entalphy of products.
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What happens during an Exothermic reaction?
Heat energy is given off. More energy is required to break bonds than is required to form new bonds. Delta H is negative.
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What happens during an Endotermic reaction?
Heat energy is taken in. More energy usrequired to form new bonds than is required to break existing bonds. Delta H is Positive.
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What is Bond enthalpy?
The energy required to break the bond between two atoms , it is also the same amount of energy gven out to the surroundings when a bond is formed. Mean bond enthapies arealways exothermic.
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Why does the value for bond enthalpies change?
Beause the energy required to break an induvidual bond can change depending on where it is.
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What is Standard enthalpy change?
The enthalphy change we a reaction occurs in molar quantities under standard conditions in standard states.
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What is Standard enthalpy change of formation?
The enthalpy chan when one mole of a substance is formed, in standard sate/conditions.
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What is Standard enthalpy change of Combustion?
Enhalpy change when one mole of a substance is completely burned in oxygen in standard states/conditions.
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State hess' law.
The total enthalpy change for a reaction is always the same, no matter which route is taken.
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Whatis rate of reaction?
A measurement based on the mass of reactant consumed in a chemical reaction during a given period of time.
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What is collison theory?
For a reaction to take place between two particles, they must collide with enough energy to break bonds. It must also take pace between the parts of the moleclethat react together (correct orientation).
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Why do most collisions between partcles not lead to reaction?
They either do not have enough energy or are in the wrong orientation.
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What is activation energy?
The minimum energy needed to start a reacton. This is enough energy to break bonds.
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How does temperature affect reaction rate?
The number of molecules is the same, but they have an increased kinetic energy.Therfore a higher percentage of collisions will result in reaction.
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How does concentration affect reaction rate?
There is a greater number of particles, so therefore they are closer together meaning that more collisionswill occur.
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How do Catalysts work?
They increase rate of reaction by providing a different pathway for the reactio with a lower activation energy. They are not used up in the reaction.
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What is Dynamic equilibium?
It is when the forward rate of reaction is equal othe rate of backward reaction.
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What are the conditions for equilibrium?
CLOSED SYSTEM. Equilibrium is reached when properties like temperature, pressure and concentration remain constant.
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What is Le Chatelier's principle?
If there's a change in concentration, pressure or temperature, the equilibrium wil move to counteract the change.
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How does changing concentration affect equilibrium?
By increasing the concentration of the reactant, the equilibrium will try to get rid of extra reactants, by making more product. Increasing the concentration of the product will move equilibrium to the left, so more reactants will be produced.
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How does changing pressure affect equilibrium?
Increasing the pressure will shift equilibrium to reduce the pressure, favoring the reaction that produces fewer moles. Decreasing the pressure favours the reactionthat produces the most amount of moles.
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How changing temperature affecct equilibrium?
By increasing pressure, equilibrium will move to take in heat, thus favoring the endothermic reaction. By decreasing the pressure, equiibrium will move to give out heat, thus favouring he exothermic reaction.
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How do catalysts affect equilibrium?
Catalysts have no effect on the position of equilibrium, but they allow equilibrium t be reachd more quickly.
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What are the conditions for ethanol production?
TEMPERATURE: 300 degrees, lower temperatres favour the forward reaction,but lower temperatures mean a slower rae of reaction. PRESSURE: 60-70 atm higher pressues favour the forward reacion, but high pressures are expensive to produce.
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Whatare the conditions for methanol production?
PRESSURE: 50-100 atm, high pressues favourthe forward reaction. TEMPERATURE: 250 degrees CATALYST: copper, zinc and aluminium oxde.
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Why are Alkenes very reactive?
Because there are wo pairs of electrons inte carbon double bond , alkenes have a high electron density, making them very reactive.
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What is an Electrophile?
A species that accept an electron pair.
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What is Nucleophile?
A species that accepts an elctron pair.
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What is a free radical?
A species that conains a single lon electron. They are very reacitve.
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What are Stereoisomers?
They have the same structural formula but a different arrangement in space. Stereoisomers happen when the two double bonded carbon atoms have different atoms or groups attached to them.
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What are the two types of Stereoisomer?
E-isomer (different) ad Z-isomer (same)
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How can Alkenes be made from Alcohols?
Alcohols can be dehydrated to from alkenes. The conditions are concentrated sulfuric acid /phosphoric acid at 180 degrees under reflux.
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Why is the dehydration of alcohols a good way to make Alkenes?
Alcohols can be made from renewable sources whereas alkanes are obtained from crude oil which is a finite resource and damaging to the environment.
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Describe the process of fermetation to produce ethanol.
Reagants: Glucose Conditions:37 degrees,yeast Rate of reaction: slow Quality:impure Process/cost: batch process with cheap equipment.
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Describe the process of the hydration of ethene to produce ethanol.
Reagant:ethene Conditions:catayst (phosphoric acid),temp 300 degrees, pressure 70atm. Rate:fast Quality: pure Process/costs:Continuous but expesive.
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What is a biofuel?
A fuel made from biological material that has recently died. Ethanol is considered to be carbon neutral, because the carbon dioxide released was removed by the crop as it grew.
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What are the conditions and reagants for the partial oxidation of primary alcohol?
Conditions: distill reagants: acidified potassium dichromate.
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What are the conditions for the full oxidation of a primary alcohol?
Reflux
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What are the conditions for the oxidation of secondary alcohols?
Reflux
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Why can't tertiary alcohols be oxididsed?
Because they do not react as they are too stable. They can only be oxidised by burning.
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How do you distinguish between a Ketone and Aldehyde?
Tollen's test: tollen's reagant (a silver amine ion) a siler mirror forms if a aldehyde is present.
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How are esters formed?
Alcohol + carboxylic acid = ester + water.
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What is fragmentation?
The bomarding of electrons makes some of the molecular ions break upinto fragments. The fragmens that are ions show up on the the mass spectrum, makina framentatio pattern.
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How is an Infa red spectra produced?
A beam of IR radiation ispassed through a sample of a chemical. The IR radiation is absorbed by the Covlent bonds in the molecules, increasin their vibrational energy. Bonds between different atoms/in different places absorb different freqencies.
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What is the fingerprint region?
The region between 1000cm^-1 and1500cm^-1, it is unique to a particular compaund.
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How does Infa red abosrption contribute to global warming?
grenhouse gases have bonds that are really good for absorbing infared energy, so if the amounts of them in the atmosphere increase, it leads to global warming.
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What is Oxidation?
A loss of electrons (OIL)
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What is reduction?
A gain of electrons (RIG)
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What is a reducing agent?
The reactant which donates electrons and gets oxidised.
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What is an oxidising agent?
The reactant that accepts electronsand is reduced.
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What is Oxidation state?
The total number of electrons it has donated or accepted.
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What is the oxidation state of an uncombined element?
0
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What does a positive oxidation state indicate?
A loss of electrons.
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What does a negative oxidation state indicate?
A gain of electrons.
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What is the order of oxdation states?
123FHOCl
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What is the boiling point trend down group 7?
The boiling points of the halogens increase down the group. The strength of the Van Der Waals forces increase as the size/relative mass increases.
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What is the trend in elctronegativity down group 7?
It decreases because there are more electrons between the outer shell and the nucleus, so there will be more electron shielding.
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What Happens when halogens are oxidised?
They gain an electron ie they are oxidising agents.
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What is Disproportionation?
When an element is both oxidised and reduced in a single chemical reaction.
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What is a use of chlorine?
To purify water. But it irritaes the respiratory system, therfore chloric acid is an alternative.
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How does reducing power change down the group?
It increases because the further away the outer shell is from the nucle, the more electron shielding there is, so an electron is lost more easily.
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What is the test for Halides?
Add dilute nitric acid and then add silver nitrate. Further test is to add dilute/concentrated ammonia.
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What is the trend in atomic radius down group 2?
It increases becuase the number of inner electrons is increasing.
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What is the trend in ionisation energy down group 2?
It decreases because the increase in nuclear charge is offset by the number of inner electrons. Also distance increases so an electron becomes easier to remove.
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What isthe trend in melting point down group 2?
Generally it decreases. The number of delocalised electrons remains he same but the ionic radius increases, so the attraction between the delocalised electrons and the metal cations decreases.
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How reactive is Berylium?
It hdoes notreact with water or steam because it has a srong resisan oxide layer on its surface.
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How reactive is magnesium?
It burns in steam to produce white magnesium oxide and hydrogen gas. Very clan magnesium ribbon has a very slight reaction with cold water. After several minutes, some hydrogen bubbles will form.
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How reactive are Calcium, Strontium and Barium?
They all ract with cold water to give the metal hydroxide and hydrogen.The reactions become easier as the energy needed to form a positive ion falls. This is because of the decrease in ionisation energy= lower activation energies.
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How does solubility of group 2 hydroxides change down the group?
It increases
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How does solubility of group 2 sulfates change down the group.
Solubility decreases.
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What is Barium meal?
Barium sulfate, it is used to diagnose gastro problems. Barium sulfate is opaque to X-rays, so when swallowed it will so soak tissues so they will show up on an X-ray.
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What is an ore?
A natural substance that a metal can be economically extracted from.
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How is a metal extracted from a Sulfide ore?
it is turned into an oxide by roasting in air. This produces sulfur dioxide, which can contribute to acidrain. This can be reacted with sulfuric acid and oxygen to produce sulfuric acid.
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What are the raw materials for the extraction of Iron from Iron (III) oxide?
Iron ore, coke, limestone at 700 degrees.
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How is Manganese obtained from Manganese (IV) oxide?
It can be reduced by Coke or Carbon monoxide. Conditions are 1200 degrees.
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How is copper obtained from copper carbonate?
1) reduction of Malchite with coke 2) Heating until it decomposes into copper (II) oxide and then reduction with coke.
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How is Tungsten extracted from its ore?
By reduction with Carbon, but that can leave impurities which make the metal brittle. It can be reduced using hydrogen but this is highly explosive and much more expensive. (conditions 700 degrees)
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How is Aluminium extracted from its ore?
By electrolysis, as it is too reactive to extract by reduction using carbon. However the anode ha to be replaced frequently because of the carbon reacting with oxygen produced.
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How is Titanium extracted from its ore?
The ore is converted to Titanium (IV) chloride by heating at 900 degrees with carbon ad chlorine gas. Then it is purified by fractional distillation under an argon atmosphere. Then it is reduced in a furnace with Na or Mg (1000 degrees).
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What are the advantages of recycling metals?
Reduces waste sent to landfill. Saves raw materials. Saves energy. Reduces carbon emissions. Reduces damage to the landscape through mining.
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What are the disadvantages of recycling metals?
Collecting/Sorting metals can be difficult and expensive. The purity or recycled metals varies. Energy is still needed, producing carbon dioxide. It may not produce a constant supply to meet demand.
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How is Scrap iron used to extract copper?
Copper ores are converted into solutions containing copper (II) ions. This is done by spraying with dilute acid in the presence of Thiobacillus ferroxidans (bio leaching) then copper is reduced by scrap iron.
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How do you calculate the enthalpy chage?

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Enthalpy of reactants-entalphy of products.

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What happens during an Exothermic reaction?

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Card 4

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What happens during an Endotermic reaction?

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Card 5

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