c7 and c8 chemistry

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what is an exothermic reaction
tranferring the energy from the reaction to surroundings, giving off energy
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what is an endothermic reaction
tranferring energy from the surroundings to the reaction, taking in energy
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does an exothermic reaction heat up or cool down the surroundings
heat up
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does an endothermic decrease or icrease the surrounding tempurature
decrease the tempurature
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what is an example of an exothermic reaction
burning fuels, combustion of methan gas, it burns and gets oxidised and releases energy to it's surroundings. also neutralisation reactions (acids and alkalines)
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do the products have lower or higher energy content than reactants in exothermic reactions
lower
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why do warm blooded animals rely on exothermic reactions
for respiration, to keep their body tempuratures steady
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what is an example of an endothermic reaction
citric acid + sodium hydrogencarbonate, thermal decomposition -calcium carbonate decompostion, when heated, forms calcium oxide + carbon dioxide, only takes place if keep heating calcium carbonate, also needs to absorb energy from surroundings
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in endothermic reactions, do the products have high or lower energy content than the reactants
higher, so energy is tranferred from the surroundings
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caco3 (s) > caO (s) + co2 (g) - how much energy is tranferred to the surroundings
178kg/mol
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investigating tempurature changes - REQUIRED PRACTICAL
record the initial tempuratures of any solutions and the max/min tempurature reached in the course of the reaction. the solution needs to be in a poly(styrene) cup and use a thermometer
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why is a polystyrene cup used in the required practical
as it reduces the rate at which energy is tranferred to or from the mixture
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how can exothermic changes be used
in hand warmed and self heating cans. crystillisation of a supersaturated solution is used in reusable warmers. however, disposable warmers heat surroundings up for longer
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how can endothermic changes be used
instant cold pacts for sports injuries, containing ammonium nitrate and water. when ammonium nitrate dissovles it absorbs energy from its surroundings to make it cooler
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exothermic reaction profile
the products are at lower a lower energy level than the reactants, energy tranferred to the surroundings
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what changes between the products and reactants
(the energy levels) - the difference between energy levels of reactants and energy levels of products change during the reaction
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why do the surroundings get hotter
because of an exothermic reaction
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endothermic reaction profile
the products are at a higher level than the reactants, as the reactants form the products, energy is tranferred from surroundings to mixture.
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why do the surroundings get cooler
becayse of an endothermic reaction, as it takes energy in for the reaction.
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what is needed before colliding particles of reactions have sufficient energy to cause a reaction
minimum amount of energy to start the reaction
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what is the energy needed to start a reaction called
the activation energy
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what happens if colliding reactant particles collide with less energy than the activation energy
they will just bounce off each other
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what has to be supplied to break bonds
energy
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if energy is needed to break bonds, what is this reaction
endothermic, as it takes energy from the surroundings
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what happens when bonds are formed
energy is tranferred to surroundings, it is giving off energy
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if bonds produce energy when formed what reaction is this
exothermic
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what happens when hydorgen and oxygen mix
it makes water, bonds between hydrogen atoms and bonds between oxygen atoms have to be broken so water can be formed
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does this process of breaking hydrogen, oxygen and making water happen in sequence
no, not all break then all form, the bond breaking and making happens at the same time, but you need to look at the energy required to break bonds and the energy released to see the overall energy change
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hat does Breaking Bonds do
aBsorBs energy - endo
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what does foRming bonds do
Releases energy - exo
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what is the reaction if the energy released when new bonds are formed is more than the energy needed to break the bonds in reactants
exothermic, it uses less, and gives off more to the surroundings
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what is the reaction when the energy needed to break the bonds in the reactants is more than the energy released when new bonds are formed
endothermic, it takes more energy in than it returns
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what is the energy needed to break the bond between two atoms called
bond energy
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if the energy change is negative what is the reaction
exothermic
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how do you caculate energy change for a reaction
how much energy is needed to break the bonds (reactants) and how much energy is released when a bond is formed (products)
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what does a rate of reaction tell you
it tells you how fast the reactants turn into products
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how do you work out the rate of reaction
finding out how quickly the reactants are used up, or how quickly the product is made
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what is measuring the decrease of a reaction mixture
measuring the rate at which the mass of the reaction changed if it gives of a gas, mass decreases, use a balance, marble chips + hcl + cotton wool (top of flask) measure at regular time intervals. mass of reacting mixture decreases
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what is measuring the increasing volume of gas given off
if a reaction produces a gas, you collect the gas and measure the volume given off at time intervals. reaction mixture in conical flask with gas syringe. the volume increases over time.
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what is measuring the decreasing light passing through a solution
some reactions in a liquid make an insoluble solid (precipitate) making a cloudy solution, measuring when the precipitate appears will show the rate of reaction. light transmitted decreases with time
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what does a steeper line show you
steeper the line + faster rate of reaction
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how do you calculate the mean rate of reaction
mean rate of reaction= quantity of reactant used / time (OR) mean rate of reaction = quantity of product formed / time
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what does the gradient tell you
the rate of that reaction at that given time
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what does a steeper gradient mean
the faster the reaction
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what 4 things affect a rate of reaction
tempurature, surface area of solids, concentration of solutions/pressure of gases, and presence of catalyst
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what is the collision theory
reactions can only take place when particles (atoms,ions,molecules) of reactants come together. they have to bump together and collide with enough energy to cause a reaction to take place
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when is a reaction more likely to happen, what two things do you have tlo increase
increase the frequency of reacting particles collliding with each other, increase the energy they have when they collide
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what happens if you increase the chance of particles reacting
also increases the rate of reaction
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what does a solid affect in a reaction
the rate of which it happens
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what happens in a large solid when it reacts
in a large lump of solid, the particles are not in contact with the reactant particles in the solution, cannot react. particles inside solid, have to wait for particles on surface to react first.
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what happens if a small solid when it reacts
each tiny piece of solid is surrounded by a solution, many more particles of this solid is exposed and able to react at any time. this means the reaction can take place quicker because nothing has to wait to react.
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how can you compare solids with different surface areas
by look at the surface area to volume, the smaller the size of pieces of the solid, larger the surface area to volume ratio
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if the solid has a larger SA:V ration what does this do to the reaction
the faster the reaction, as more particles on the surface are exposed
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what happens if a side of a cube decreases by 10
the SA to V increases by 10,
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what happens if the solid gets larger
the sa to v decreases
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does a larger surface area increase or decrease the freqency of collisions
increase
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what happens to the rate of reaction if you increase tempurature
increases the rate of reaction
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why does the rate of reaction increase when tempurature increases
collision theory - particles collide more often, and they collide with more energy
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what happens when you heat a substance
energy is tranferrred to its particles
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when particles collide more frequently what does this mean to the rate of reaction
bigger chance to react, and increases rate of reaction
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what does it mean if the particles have more energy
they move quicker, collisions are more energetic.
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what happens if you increase the temperature of a reacting mixture
a higher proportion of collisions will result in the reaction taking place at any time. as a higher proportion of particles ahve higher energy greater than the activation energy
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what happens if an increased proportion of particles exceed the activation energy
greater effect on the rate of reaction than the increased frequency of collisions
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when increasing the concentration of reactants what affect does this have on the rate of reaction
it increases as there are more particles of reactants moving around the same volume of solution. the particles closy packed particles will more likely to collide, increaded frequency of collisions, higher rate of reaction
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concentration rate of reaction - REQUIRED PRACTICAL
investigating effect of changing conc by reacting marle chips and different conc of hcl.
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what is the balanced equatiopn for hcl and marble chips and hcl in the REQUIRED PRACTICAL
CaCO3 (s) + 2HCl (aq) > CaCl2 (aq) + CO2 (g) + H2O (l)
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how do find the rate of reaction in the REQUIRED PRACTICAL
plotting the volume of carbon dioxide gas given off as the reaction prgresses over time. measure the volume of gas at regular time intervals using conical flask and gas syringe.
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what happens to the mass if a higher conc of hcl was use REQUIRED PRACTICAL
line steeper, faster rate of reaction, more mass lost quicker
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if a lower conc of hcl was used, what would happen to the mass
less mass lost, slower rate of reaction, line gradually falls
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what is a catalyst
a substance that changes the rate of reaction, not changed chemically, it isn't used up in the reaction, and can be used again and don't increase the frequency of collisions
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how do catalysts work
they provide an alternative pathway to the products, with a lower activation energy than without the catalyst. so, a higher proportion of reactant particles have sufficient energy to react, so the frequency of EFFECTIVE collisions increases
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a reaction profile with a catalyst and without
the reaction without the catalyst has a higher activation energy
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pros and cons of a catalyst
quicker and effective and re-usable but can be expensive but then if you don't use one it could be more expensive to get energy without a catalyst (increasing temp or pressure) save money and help the environment
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how do catalysts help the environment
high temp/pressures invovle burning fossil fuel, so lower temps and pressures conserves the non renewable resources, stops co2 entering atmosphere when burnt, combats climate change
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why do catalysts used in chemical plants eventually not work
they become 'poisoned' as impurities in the reaction mixture combine with catalyst and stop it working properly
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what is a reversible reaction
the reactants react to make the products and the products can react to make the original reactants
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what is an example of a reversible reaction
heating ammonium chloride, to break it down into ammonia gas and hydrogen chloride gas. when the gases cool down, they recombine to form the white solid ammonium chloride again
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in a reversible reaction is it endothermic or exothermic or both
one will be endo / one will be exo
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what happens if the reaction tranfers energy to the surroundings going to the products
it will take in exactly the same amount of energy from the surroundings going back to the reactants
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what is a closed system
where no reactants or products enter or leave
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what happens in a reversible reaction when the concentration builds up
when the conc of products build up, the rate at which they react to re-form reactants increases. as this happens the foward reaction decreases.
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why does the foward reaction decrease when the products build up to reform the reactants
as the conc of reactants is decreasing from original maximum value. eventually both foward and reverse reactions happen at the same time just opposite directions
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what does it mean if both reactions in different directions happen at the same time
the reactants are making the products at the same rate the products are making the reactants, overall there is no change of amount of products/reactants - reaching equilibrium
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what is eqilibrium
the rate of the foward reaction = the rate of the reverse reaction
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what is a dynamic eqilibrium
where foward and reverse reactions are taking place continuously
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Le chateliers principle
he noticed that whenever a change in conditions is introduced to a system at equilibrium , the position of eqilibrium shifts. the changes can be in conc,temp,pressure
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what happens to the shift of equilibrium if you increase the conc of reactant
the point will shift to the right, in favour of the products.
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how do you determine which way the shift goes
it will go to the opposite side the is changed, it opposes the change that is introduced
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what happens if the tempurature increases
the equilibrium shifts to reduce the temp, favours endothermic reaction
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what happens if the tempurature decreases
favours exothermic
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what is an endothermic reaction

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tranferring energy from the surroundings to the reaction, taking in energy

Card 3

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does an exothermic reaction heat up or cool down the surroundings

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Card 4

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does an endothermic decrease or icrease the surrounding tempurature

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Card 5

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what is an example of an exothermic reaction

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