IGCSE CHEMISTRY :VERIFIED NOTES Edexcel GCSE Chemistry Rate of Reaction

IGCSE CHEMISTRY :VERIFIED NOTES Edexcel GCSE Chemistry Rate of Reaction Explain why increasing the temperature increases the rate of reaction? This means that particles have more energy so there are more frequent collisions. These collisions are more successful What are catalysts? a substance that increases the rate of a chemical reaction without being used up, it is chemically unchanged. Explain in terms of energy involved in the breaking and making of bonds why some reactions are exothermic? Energy is needed to break bonds and the energy released when these bonds are broken. More energy is released than needed. Explain why in a reaction, the reactants are used up and the rate of reaction decreases? As the reactants are used up, there are fewer particles left to react. This means that there will be a lower frequency of collisions, so fewer particles will react in a given time. Explain, in terms of bonds and energy why a reaction would be exothermic? Breaking bonds is an endothermic process and forming bonds is an exothermic process. During this, more energy is given out than taken in What type of reaction occurs in a catalytic converter? Oxidation Explain why the catalyst is spread onto a honeycomb structure rather than used as large pieces? This means that it has a large surface area so there are more frequent collisions with the catalyst. What is the equation for the rate of reaction? Amount of reactant used or amount of product formed / time What is activation energy? The minimum amount of energy needed for a chemical reaction to occur. How does pressure affect the rate of reaction? Increasing the pressure increases the rate of reaction as the reactant particles are squeezed together so more frequent collisions occur. How do you measure the rate of reaction when a gas is given off? Measure 40cm3 of dilute hydrochloric acid into a conical flask. Add 5g of small marble chips to the flask. Stopper the flask and start the stop clock. Record the total volume of gas produced after every 30 secs until the reaction is finished. Repeat the experiment using 5g of larger marble chips. How can you measure the rate of reaction by observing a colour change? Decide on 4 temperatures to investigate. Place 10cm3 of sodium thiosulfate solution and 40cm3of water into a conical flask. Measure out 5cm3 of dilute hydrochloric acid into a test tube. Clamp the conical flask in a water bath. Also place the test tube in a water bath. Record the chosen temperature. After 5 mins, remove the flask and place it onto a white piece of paper marked with a cross. Add the acid to the thiosulfate and start the stop clock. Looking down from above, stop the clock when the cross disappears. Note this time and the final temperature. Repeat the steps for the other chosen temperatures. Suggest possible sources of errors in the gas investigation The upside down cylinder water measurement may alter and effect the results, so it may not be as accurate. Suggest changes to the method that could improve the reliability of the results of the gas investigation Measure the volume of gas produced for a long time. For the gas investigation, how would you know when the reaction is complete? No more gas would be formed Describe how you would use a tangent line to estimate the reaction rate? Draw a tangent line. Calculate the rate by dividing the change in volume by change in time. Chose 2 points on the tangent and calculate the change in volume that happens for the change in time.