SC18 & SC19 - Rates of Reaction / Heat Energy Changes in Chemical Reactions ✓

The speed at which reactants turn into products

• Works for reactions where a gas is produced • Set up a liquid in a conical flask • Push a gas syringe to 0 and attach it to a bung • Add the granules of the other chemical into the conical flask and immediately attach the bung • Also set off a timer. Every 10 seconds record down the value red on your gas syringe • Repeat and take the average of concordant results • use the average results and plot them on a graph

• Concentration on y axis time on the x axis • Products start at 0 and have an increasing positive curve • Reactants start high and have an increasing positive curve till 0 • Both curves will plateau (flatten out) at the same point

• Work for reactions where one of the products are gases • Place the conical flask on the balance at set it to 0 • Add the liquid being used into the conical flask and then add the other chemical • Quickly record down the starting mass and cover the flask with cotton wool to stop acid form spitting • Set off timer and record down the mass every 10 seconds • Repeat and take the average of concordant results • Plot a graph using the average results

• Temperature • Pressure • Concentration • Surface areas/volume ratio • Presence of a catalyst

• An increase in temperature gives the reactant particles more kinetic energy meaning they move around more • This means there will be more frequent successful collisions and more particles will have the required level of energy to react

The minimum amount of energy required for a reaction to occur

• An increase in concentration means more particles in a fixed volume • This means that that successful collisions will be more frequent as particles are closer together

• An increase in pressure means the same amount of particles in a smaller volume • This means that that successful collisions will be more frequent as particles are closer together

• An increase of the surface area to volume ration means for a fixed volume, there is more surface area. • This leaves more of the surface exposed • This means that collisions have more surface to occur on and so successful ones occur more often

• A catalyst increases the rate of reaction without being used up by lowering the activation energy required • This means more particles will have the required activation energy and collisions will more frequently be successful

• Set up the apparatus with a clamp holding an upturned measuring cylinder over a trough containing water • Have a delivery tube attached to a bung lead up to the cylinder and record the starting value • Put 40cm³ of hydrochloric acid (Use the same concentration throughout) into a flask. • Measure out 5g of small marble chips • Add the marble chips to the flask and immediately close it with the bung • Start the timer and record the value of gas produced every 30 seconds until the reaction has finished • Repeat 3 times and take the average of concordant results. Use this to plot a graph • Repeat all steps but using large marble chips of the same mass and plot these results on a graph

• Measure out 50cm³ of sodium thiosulfate into a conical flask • Measure out 5cm³ of hydrochloric acid into a test tube • Place the conical flask and test tube in a water bath of a set temperature • After the chemicals have acclimatized (around 5 minutes), take them out and add the hydrochloric acid into the flask • Place it on a piece of white paper and immediately start the timer • Stop the timer once it has turned cloudy and the cross is no longer visible • Repeat with different temperatures of the water bath and plot a graph

Catalysts increase the rate of reaction without being used up

• Catalysts provide an alternate reaction pathway by which a lower level of activation energy is required. • This means that more particles will be able to reach the required activation energy and therefore successful collisions will be more frequent

The peak will be a lot lower however it will being to rise and stop falling at the same places

• By increasing the rate of reaction, there will be more products produced in a fixed amount of time. • Also, as catalysts don’t get used up, they can be used multiple times. • This means that the process is more profitable

• Combustion inside a car produces toxic gases • A catalytic converter uses catalysts of palladium and platinum to convert theses into less harmful gases • The catalysts are spread over a thin honeycomb structure because: • Increased surface increases the efficiency of the cat con. • As little catalyst as possible is used as the metals are very expensive

• Enzymes are large protein molecules that act as biological catalysts • They have specifically shaped active sites to the shape of their reactant molecules (substrates) • Changes in temperature can denature the active site, changing its shape • They are used in man things e.g. production of alcohol You should know this in more detail for biology anyway but yeah….

• Exothermic reactions: • Energy from stores in bonds is transferred to surroundings • Measured temperature will be hotter • Products will have less energy • Endothermic reactions: • Energy is taken in from surroundings is transferred to stores in bonds • Measured temperature will be cooler • Products will have more energy

• Exo: • Horizontal line for reactants • vertical arrow down • lower horizontal line for products • Endo: • Horizontal line for reactants • vertical arrow up • higher horizontal line for products

• Neutralisation: Acid + base • Displacement: More reactive element displaces a less reactive element that was part of a compound

• Precipitation: Two soluble reactants form a soluble product • Dissolving: When you dissolve something <strong>#helpful</strong>

• Place one of your chemicals in the polystyrene cup (in a beaker for support) and measure the starting temperature. • Add the other chemical and then place the lid and push the thermometer through the top. • Record the final temperature once the reaction has stopped. • Lid used to limit heat loss and polystyrene is a poor conductor of heat • A reduction of heat means it is endothermic while an increase of heat means it is exothermic