Topic 18 - Rates of Reaction Flashcards
7.1 - Core Practical : Investigate the effects of changing the conditions of a reaction
Method 1 - measuring the production of CO2 in the reaction (and how it affects the reaction rate) between HCL and different marble chips with different surface areas.
Measure 50cm3 of HCL into a conical flask.
Add 5g of small marble chips and immediately stopper the flask and start timer,
Note the volume of gas produced in 30sec intervals until reaction is finished.
Repeat the experiment using larger 5g marble chips.
Method 2 - Investigating the effect of temperature on the rate of reaction between sodium thiosulfate and HCL, observing a colour change in the reaction.
Place 50cm3 of sodium thiosulfate solution in a conical flask.
Measure out 5cm3 of dilute HCL in a test tube.
Clamp conical flask in a water bath at a certain noted temperature, place test tube in a rack in the same water bath.
After 5mins, remove the flask and place it on a piece of white paper with a cross
Add the acid to the thiosulfate and start the timer.
Stop the clock when the cross disappears.
Note time and temperature of the mixure.
Repeat at other temperatures between 20 and 50 degrees.
7.2 - What are the practical methods for finding the rate of a reaction?
The rate of a reaction is the speed at which reactants become products.
It can be found using this equation : Amount of reactants or products/time
Quantity of reactants can be found by carrying out the reaction on a weighing scale and measuring the mass lost.
Quantity of products can be measured using a gas syringe if it is a gas.
7.3 - What has to happen for two particles to react?
Chemical reactions happen when reactant particles collide with eachother with enough energy to react.
The minimum energy to react is the activation energy.
During successful collisions, this energy breaks bonds so atoms can be rearranged to make new substances which are the products.
Reactions which release energy are exothermic while those that take in energy are endothermic.
Exothermic reactions break bonds and this energy supplies the activation energy, although it needs a spark of energy.
Endothermic reactions only will not carry on without a continuous energy supply.
7.3 - How does the energy and frequency of collisions affect the rate of reaction?
Reaction rates are increased when the energy of the collisions are increased.
More collisions occur if the particles are in a closer range as the frequency of collisions increase.
More collisions are successful if more particles have the activation energy.
7.4 - Explain how changes in some factors change the rate of reaction?
Increasing the temperature increases the rate of reaction. This is because temperature is the average KE of particles.
Therefore the reactant particles speed up as they have more energy and collide more frequently with the activation energy.
Increasing pressure increases the rate of reaction.
This is because number of particles in a given are is higher, so the FSCs of particles are more often.
Increasing the concentration of solutions increases the rate of reaction.
This is because there are more reacting particles in the same volume and therefore more collisions occur.
Increasing the surface area to volume ratio by decreasing the size of the solid while keeping the volume the same increases the rate of reaction.
This is because there is more surface area for collisions, so they are more frequent.
7.5 - How do you interpret graphs of a reactant against time?
The gradient indicates the rate of the reaction.
Reactions are normally steeper at the start of the reaction as this is when the reactant concentration is greatest meaning a faster rate of reaction.
7.6 - What is a catalyst?
Substances that speed up the rate of reaction without being permanently changed themselves and without altering the products of the reaction.
7.7 - Explain how the addition of a catalyst affects the rate of reaction?
Catalysts are mostly used in industry where they provide alternative reaction route which requires less activation energy.
Reaction profiles show the effect of a catalyst by comparing an uncatalaysed reaction with a catalysed one.
The catalyst doesn’t affect overall energy change but as less energy is needed to start the reaction, more reactant particles have enough energy so more collisions are successful. This increases the rate of reaction.
7.8 - What are the uses of catalysts?
In catalytic converters are used in car exhausts. The presence of lowers activation energy to convert harmful gases to harmless gases. The metals used are expensive but don’t need to be replaced as they a
7.8 - What are the uses of catalysts?
In catalytic converters are used in car exhausts. The presence of lowers activation energy to convert harmful gases to harmless gases. The metals used are expensive but don’t need to be replaced as they a
7.8 - What are the uses of catalysts?
In catalytic converters are used in car exhausts. The presence of lowers activation energy to convert harmful gases to harmless gases. The metals used are expensive but don’t need to be replaced as they a
7.8 - What are the uses of catalysts?
In catalytic converters are used in car exhausts. The presence of lowers activation energy to convert harmful gases to harmless gases. The metals used are expensive but don’t need to be replaced as they aren’t used up.
Enzymes are large complex proteins that act as catalysts in biological reactions. Each enzyme molecule has a part called an active site, the reactants fit the shape of the active site. So a catalyst only catalyses a specific reaction. Catalysts are sensitive to temperature as this can denature the molecules so they won’t work.
Alcoholic drinks are made using an enzyme in yeast. This enzyme catalyses the reaction where glucose is converted into ethanol and carbon dioxide.
