C8- Rates and equilibrium
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4 ways to monitor progress of a reaction
-Volume of gas produced -Mass lost due to gas being formed -Changes in colour or opacity -Time for solid to disappear
How to calculate the rate of reaction at a specific time on a graph
-Draw a tangent to the curve at specific time -Draw a right-angled triangle -Calculate gradient by change in y / change in x -Include units
Steeper gradient, reaction is…?
Steeper the gradient, faster the rate of reaction
3 types of practicals to calculate rate of reaction
Measure decreasing mass Measure increasing volume of gas Measure decreasing light passing through
Two equations for rate of reaction
Amount of reactant used / time Amount of product made / time
Describe rate of reaction graph
-Fastest rate at beginning, maximum number of moles (0s) -Rate decreases over time as reactants are used up -Rate reaches 0 when one reactant is used up
5 factors that affect rate of chemical reactions
-Temperature -Surface area of solids -Concentration of solutions -Pressure of gases -Including catalyst
Collision theory
For a reaction to occur, reactant particles must collide with sufficient energy
Activation energy
Minimum energy that particles must have before they can react
3 general ways to increase rate of reaction
-Increase frequency of collisions -Increase energy of collisions -Reduce energy required for a reaction
What category does a higher SA:volume ratio increase?
Increases frequency of collisions
How to investigate the surface area affecting rate of reaction by volume of gas produced?
Measure 20cm3 of 1mol/dm3 HCl into beaker, add carbonate chips. Quickly place a bung connected to gas syringe, start timer. Wait 30s, record volume of gas. Repeat w powder. Higher vol of gas, faster rate of reaction.
Why does increasing SA:Volume ratio increase rate of reaction?
-Increases proportion of particles on surface -Higher frequency of successful collisions -Increase rate of reaction
What has the greatest effect on the rate of reaction: Increased frequency of collisions or increased energy of collisions?
An increased proportion of particles exceeding the activation energy
Why does an increased temperature increase rate of reaction?
-Particles have more KE -Move faster, more frequent collisions -Larger proportion of particles have the activation energy -Greater frequency of successful collisions
What does a higher concentration of reactants increase? and why?
More particles moving around in the same volume, increase frequency of collisions.
What does a higher pressure increase? and why?
Same number of particles in smaller volume, closer together. Increase frequency of collisions
Catalyst
Chemical substance that increases rate of reaction without being used up
How does a catalyst increase rate of reaction?
Provide an alternative reaction pathway, with a lower activation energy
2 key advantages of catalysts
-Save money, no paying to provide high energy -Help environment, burning less fossil fuels
Reversible reaction and key symbol?
Where the products can react together to make the original reactants again Two half arrows
Reversible reaction observations with ammonium chloride
When heated ammonium chloride forms ammonia gas and hydrogen chloride, they then cool at top of tube before reacting with each other again to form ammonium chloride solids at the top
How to investigate the effect of concentration on the rate of reaction
Measure 20cm3 of thiosulfate with a concentration of 8mol/dm3. Place thiosulfate in conical flask on top of a cross. Add 5cm3 HCl to conical flask, swirl once, start stopclock. When cross no longer visible, stop stopclock. Record time taken, calculate rate by using 1/time for reaction. Repeat with dif concs. Plot time against conc on a graph
In reversible reactions what type of reaction are they? Therefore the energy transferred each way?
One is endothermic and the other is exothermic Amount of energy transferred to surroundings is the same amount taken back in