Edexcel GCSE Chemistry Reversible Reactions and Equilibria Notes PDF

Edexcel​ ​GCSE​ ​Chemistry Topic​ ​4:​ ​Extracting​ ​metals​ ​and equilibria Reversible​ ​reactions​ ​and​ ​equilibria Notes www.pmt.education 4.13​ ​Recall​ ​that​ ​chemical​ ​reactions​ ​are​ ​reversible,​ ​the​ ​use​ ​of​ ​the​ ​symbol​...

Edexcel​ ​GCSE​ ​Chemistry Topic​ ​4:​ ​Extracting​ ​metals​ ​and equilibria Reversible​ ​reactions​ ​and​ ​equilibria Notes www.pmt.education 4.13​ ​Recall​ ​that​ ​chemical​ ​reactions​ ​are​ ​reversible,​ ​the​ ​use​ ​of​ ​the​ ​symbol​ ​⇌​ ​in equations​ ​and​ ​that​ ​the​ ​direction​ ​of​ ​some​ ​reversible​ ​reactions​ ​can​ ​be​ ​altered by​ ​changing​ ​the​ ​reaction​ ​conditions In​ ​some​ ​chemical​ ​reactions,​ ​the​ ​products​ ​of​ ​the​ ​reaction​ ​can​ ​react​ ​to​ ​produce the​ ​original​ ​reactants o These​ ​are​ ​called​ ​reversible​ ​reactions o The​ ​direction​ ​of​ ​the​ ​reaction​ ​can​ ​be​ ​changed​ ​by​ ​changing​ ​the​ ​conditions aka​ ​if​ ​the​ ​forwards​ ​reaction​ ​takes​ ​place​ ​in​ ​hot​ ​conditions,​ ​lowering​ ​the temperature​ ​can​ ​allow​ ​the​ ​reverse​ ​reaction​ ​to​ ​take​ ​place E.g.​ ​The​ ​Haber​ ​Process:​ ​nitrogen​ ​+​ ​hydrogen​ ​⇌​ ​ammonia the​ ​⇌​ ​symbol​ ​is​ ​used​ ​to​ ​show​ ​that​ ​a​ ​reaction​ ​is​ ​reversible 4.14​ ​Explain​ ​what​ ​is​ ​meant​ ​by​ ​dynamic​ ​equilibrium equilibrium: o rate​ ​of​ ​forward​ ​reaction​ ​=​ ​rate​ ​of​ ​backward​ ​reaction o concentration​ ​of​ ​reacting​ ​substances​ ​stay​ ​the​ ​same dynamic​ ​equilibrium: o once​ ​the​ ​forward​ ​and​ ​backward​ ​reaction​ ​reach​ ​equilibrium,​ ​they​ ​keep going 4.15​ ​Describe​ ​the​ ​formation​ ​of​ ​ammonia​ ​as​ ​a​ ​reversible​ ​reaction​ ​between nitrogen​ ​(extracted​ ​from​ ​the​ ​air)​ ​and​ ​hydrogen​ ​(obtained​ ​from​ ​natural​ ​gas) and​ ​that​ ​it​ ​can​ ​reach​ ​a​ ​dynamic​ ​equilibrium Used to manufacture ammonia, which is used to produce nitrogen-based fertilisers The​ ​raw​ ​materials​ ​for​ ​the​ ​Haber​ ​process​ ​are​ ​nitrogen​ ​and​ ​hydrogen. Nitrogen is obtained from the air and hydrogen may be obtained from natural gas​ ​or​ ​other​ ​sources. The purified gases are passed over a catalyst of iron at a high temperature (about​ ​450​ ​°C)​ ​and​ ​a​ ​high​ ​pressure​ ​(about​ ​200​ ​atmospheres). Some​ ​of​ ​the​ ​hydrogen​ ​and​ ​nitrogen​ ​reacts​ ​to​ ​form​ ​ammonia. The reaction is reversible so ammonia breaks down again into nitrogen and hydrogen. nitrogen​ ​+​ ​hydrogen​ ​⇌​ ​ammonia www.pmt.education  4.16​ ​Recall​ ​the​ ​conditions​ ​for​ ​the​ ​Haber​ ​process​ ​as:​ ​temperature​ ​450 degrees​ ​C,​ ​pressure​ ​200​ ​atmospheres​ ​and​ ​iron​ ​catalyst 4.17​ ​(HT​ ​only)​ ​Predict​ ​how​ ​the​ ​position​ ​of​ ​a​ ​dynamic​ ​equilibrium​ ​is​ ​affected by​ ​changes​ ​in:​ ​temperature,​ ​pressure​ ​and​ ​concentration The​ ​relative​ ​amounts​ ​of​ ​all​ ​the​ ​reacting​ ​substances​ ​at​ ​equilibrium​ ​depend​ ​on​ ​the conditions​ ​of​ ​the​ ​reaction. If​ ​a​ ​system​ ​is​ ​at​ ​equilibrium​ ​and​ ​a​ ​change​ ​is​ ​made​ ​to​ ​any​ ​of​ ​the​ ​conditions,​ ​then the​ ​system​ ​responds​ ​to​ ​counteract​ ​the​ ​change. o Effects​ ​of​ ​changing​ ​conditions​ ​on​ ​a​ ​system​ ​at​ ​equilibrium​ ​can​ ​be predicted​ ​using​ ​Le​ ​Chatelier’s​ ​Principle. Effect​ ​of​ ​changing​ ​concentration: o If​ ​the​ ​concentration​ ​of​ ​one​ ​of​ ​the​ ​reactants​ ​or​ ​products​ ​is​ ​changed,​ ​the system​ ​is​ ​no​ ​longer​ ​at​ ​equilibrium​ ​and​ ​the​ ​concentrations​ ​of​ ​all​ ​the substances​ ​will​ ​change​ ​until​ ​equilibrium​ ​is​ ​reached​ ​again. o If​ ​concentration​ ​of​ ​reactants​ ​is​ ​increased​:​ ​position​ ​of​ ​equilibrium​ ​shifts towards​ ​products​ ​(right)​ ​so​​ ​more​ ​product​ ​is​ ​produced​​ ​until​ ​equilibrium​ ​is reached​ ​again o if​ ​concentration​ ​of​ ​products​ ​is​ ​increased​:​ ​position​ ​of​ ​equilibrium​ ​shifts towards​ ​reactants​ ​(left)​ ​so​ ​more​ ​reactant​ ​is​ ​produced​​ ​until​ ​equilibrium​ ​is reached​ ​again Effect​ ​of​ ​changing​ ​pressure: o In​ ​gaseous​ ​reactions,​ ​an​ ​increase​ ​in​ ​pressure​ ​will​ ​favour​ ​the​ ​reaction​ ​that produces​ ​the​ ​least​ ​number​ ​of​ ​molecules​ ​as​ ​shown​ ​by​ ​the​ ​symbol equation​ ​for​ ​that​ ​reaction. If​ ​a​ ​reaction​ ​produces​ ​a......larger volume of gas (more moles...smaller volume of gas (fewer on​ ​product​ ​side) moles​ ​on​ ​product​ ​side) An​ ​increase​ ​in​ ​pressure... Decreases​ ​yield​ ​of​ ​reaction- Increases​ ​yield​ ​of​ ​reaction- equilibrium​ ​shifts​ ​left equilibrium​ ​shifts​ ​right A​ ​decrease​ ​in​ ​pressure... Increases​ ​yield​ ​of​ ​reaction- Decreases​ ​yield​ ​of​ ​reaction- equilibrium​ ​shifts​ ​right equilibrium​ ​shifts​ ​left Effect​ ​of​ ​changing​ ​temperature: If​ ​temperature​ ​is​ ​increased​:​ ​equilibrium​ ​moves​ ​in​ ​the​ ​direction​ ​of​ ​the endothermic​ ​reaction​​ ​(e.g.​ ​if​ ​forwards​ ​reaction​ ​is​ ​endothermic​ ​and temperature​ ​is​ ​increased,​ ​equilibrium​ ​shifts​ ​right​ ​to​ ​produce​ ​more product) If​ ​temperature​ ​is​ ​decreased​:​ ​equilibrium​ ​moves​ ​in​ ​the​ ​direction​ ​of​ ​the exothermic​ ​reaction www.pmt.education  For​ ​the​ ​forwards​ ​being​ ​exo/endothermic​ ​and​ ​yield​ ​meaning​ ​the​ ​amount of​ ​product​ ​from​ ​the​ ​forwards​ ​reaction: Exothermic Endothermic An​ ​increase​ ​in​ ​temperature... Decreases​ ​yield​ ​of Increases​ ​yield​ ​of reaction-​ ​equilibrium reaction-​ ​equilibrium moves​ ​left moves​ ​right A​ ​decrease​ ​in​ ​temperature... Increases​ ​yield​ ​of Decreases​ ​yield​ ​of reaction-​ ​equilibrium reaction-​ ​equilibrium moves​ ​right moves​ ​left www.pmt.education