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Factors affecting the Speed-Rates of Chemical Reactions

3f Light initiated chemical reactions

Can light start chemical reactions? These revision notes are suitable for GCSE IGCSE O Level KS4 science chemistry students studying the effect of light on certain chemical reactions. The descriptions of experiments to do with light initiated reactions and theoretical explanations should help with homework, coursework assignments, laboratory experiment investigations 'labs' on the chemical effects of light. These notes on light induced chemical reactions are designed to meet the highest standards of knowledge and understanding required for students/pupils doing GCSE chemistry, IGCSE chemistry, O Level chemistry, KS4 science courses and can be useful primer for A Level chemistry courses. These revision notes on light catalysed chemical reactions should prove useful for the new AQA GCSE chemistry, Edexcel GCSE chemistry & OCR GCSE chemistry (Gateway & 21st Century) GCSE (9–1), (9-5) & (5-1) science courses.

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3. The Factors affecting the Rate of Chemical Reactions

3f The Effect of Light

  • CAN LIGHT AFFECT THE SPEED OF ANY REACTIONS?

  • IF IT DOES, HOW DOES CHANGE THE SPEED OF A CHEMICAL REACTION?

  • Why does increasing light intensity sometimes increase the speed of a reaction?

  • Light energy (uv or visible radiation) can initiate or catalyse particular chemical reactions.

    • As well as acting as an electromagnetic wave, light can be considered as an energy 'bullets' called photons and they have sufficient 'impact energy' to break chemical bonds, that is, enough energy to overcome the activation energy.

    • The greater the intensity of light (visible or ultra-violet) the more reactant molecules are likely to gain the required energy (activation energy) and react, so the reaction speed increases.

    • Strictly speaking the light (visible or uv) is NOT a catalyst in the sense that the photons of energy are used up in the chemical changes they induce, the photons cannot be recycled!

  • Examples:

    • Silver salts are converted to silver in the chemistry of photographic exposure of the film.

      • Silver chloride (AgCl), silver bromide (AgBr) and silver iodide (AgI) are all sensitive to light ('photosensitive'), and all three are used in the production of various types of photographic film to detect visible light and beta and gamma radiation from radioactive materials.

      • Each silver halide salt has a different sensitivity to light.

      • When radiation hits the film the silver ions in the salt are reduced by electron gain to silver

        • Ag+ + e- ==> Ag (X = halogen atom, Cl, Br or I)

        • and the halide ion is oxidised to the halogen molecule by electron loss

        • 2X- ==> X2 + 2e-

        • so overall the change via light energy is: 2AgX ==> 2Ag + X2

      • AgI is the least sensitive and used in X-ray radiography, AgCl is the most sensitive and used in 'fast' film for cameras.

    • Photosynthesis in green plants:

    • Photochemical Smog:

      • This is very complex chemistry involving hydrocarbons, carbon monoxide, ozone, nitrogen oxides etc.

      • Many of the reactions to produce harmful chemicals are catalysed or promoted by light energy.

    • The very fast reactions between (i) hydrogen and chlorine AND (ii) between chlorine and methane are both initiated by uv light. At room temperature nothing happens until violet or uv light is shone onto the mixture, then it explodes into action BUT well controlled under industrial manufacturing conditions!

      • (i) hydrogen + chlorine ==> hydrogen chloride

        • H2 + Cl2 == uv ==> 2HCl

      • (ii) methane + chlorine ==> chloromethane

        • CH4 + Cl2 == uv ==> CH3Cl + HCl

  • More details of laboratory investigations ('labs') involving 'rates of reaction' i.e. experimental methods for observing the speed of a reaction are given in the INTRODUCTION

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GCSE/IGCSE MULTIPLE CHOICE QUIZ on RATES of reaction

GCSE chemistry IGCSE chemistry revision notes on light as rate factor KS4 GCSE Science revision notes on light as rate factor GCSE chemistry guide notes on light as rate factor for schools colleges academies science course tutors images pictures diagrams for light as rate factor science chemistry revision notes on light as rate factor for revising chemistry module topics notes to help on understanding of light as rate factor university courses in science careers in science jobs in the industry laboratory assistant apprenticeships technical internships USA US grade 8 grade 9 grade10 AQA chemistry science GCSE notes on light as rate factor Edexcel chemistry science notes on light as rate factor for OCR 21st century chemistry science notes on light as rate factor OCR GCSE Gateway science chemistry notes on light as rate factor WJEC gcse science chemistry notes on light as rate factor CCEA/CEA gcse chemistry notes science O level chemistry notes for light as rate factor IGCSE chemistry revision notes on light as rate factor O level chemistry notes should prove useful for the new AQA chemistry, Edexcel chemistry & OCR chemistry GCSE (9–1, 9-5 & 5-1) science courses study chemistry at Cambridge University study chemistry at  Oxford University study chemistry at Durham University study chemistry at York University study chemistry at Edinburgh University study chemistry at St Andrews University study chemistry at Imperial College London University study chemistry at Warwick University study chemistry at Sussex University study chemistry at Bath University study chemistry at Nottingham University study chemistry at Surrey University study chemistry at Bristol University study chemistry at Cardiff University study chemistry at Birmingham University study chemistry at Manchester University study chemistry at University College London University study chemistry at Strathclyde University study chemistry at Loughborough University study chemistry at Southampton University study chemistry at Sheffield University study chemistry at Glasgow University study chemistry at Liverpool University study chemistry at Leeds University study chemistry at Queens, Belfast University study chemistry at Kings College, London University study chemistry at Heriot-Watt University study chemistry at Lancaster University study chemistry at East Anglia (UEA) University study chemistry at Newcastle University study chemistry at Keele University study chemistry at Leicester  University study chemistry at  Bangor University study chemistry at Nottingham Trent University study chemistry at Kent University study chemistry at Aberdeen University study chemistry at Coventry University study chemistry at Sheffield Hallam University study chemistry at Aston University study chemistry at Hull University study chemistry at Bradford University study chemistry at Huddersfield University study chemistry at Queen Mary, University of London University study chemistry at Reading University study chemistry at Glyndwr University study chemistry at Brighton University study chemistry at Manchester Metropoliten University study chemistry at De Montfort University study chemistry at Northumbria University study chemistry at South Wales University study chemistry at Liverpool John Moores University study chemistry at Central Lancashire University study chemistry at Kingston University study chemistry at West of Scotland University study chemistry at Lincoln University study chemistry at Plymouth University study chemistry at Greenwich University study chemistry at Liverpool Metropolitan  University gcse chemistry revision free detailed notes on effect of light on the rate of chemical reaction to help revise igcse chemistry igcse chemistry revision notes on effect of light on the rate of chemical reaction O level chemistry revision free detailed notes on effect of light on the rate of chemical reaction to help revise gcse chemistry free detailed notes on effect of light on the rate of chemical reaction to help revise O level chemistry free online website to help revise effect of light on the rate of chemical reaction for gcse chemistry  free online website to help revise effect of light on the rate of chemical reaction for igcse chemistry free online website to help revise O level effect of light on the rate of chemical reaction chemistry how to succeed in questions on effect of light on the rate of chemical reaction for gcse chemistry how to succeed at igcse chemistry how to succeed at O level chemistry a good website for free questions on effect of light on the rate of chemical reaction to help to pass gcse chemistry questions on effect of light on the rate of chemical reaction a good website for free help to pass igcse chemistry with revision notes on effect of light on the rate of chemical reaction a good website for free help to pass O level chemistry GCSE (9–1, 9-5 & 5-1) science courses

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