HOME PAGE * KS3 SCIENCES * GCSE BIOLOGY CHEMISTRY PHYSICS * ADVANCED LEVEL CHEMISTRY

Advanced level chemistry kinetics notes: Deducing activation energy from rate data

AQA Advanced A level Chemistry Edexcel Advanced A level Chemistry OCR Advanced A level Chemistry A OCR Salters Advanced A level Chemistry B

doc bDoc Brown's Advanced A Level Chemistry

Advanced A Level Chemistry

Kinetics-Rates Part 6

6.1 The Arrhenius equation

Its implications and use to calculate activation energies

and the effect of temperature on the value of the rate constant


Advanced A Level Kinetics Index

Doc Brown's Chemistry Advanced Level Pre-University Chemistry Revision Study Notes for UK IB KS5 A/AS GCE advanced level physical theoretical chemistry students US K12 grade 11 grade 12 physical theoretical chemistry courses topics including kinetics rates of reaction speeds



 

6.1 Deriving the activation energy Ea from kinetics–rates data

  • CAN YOU DETERMINE THE VALUE OF THE ACTIVATION ENERGY FOR A GIVEN REACTION?

  • IF SO, WHAT DATA DO WE NEED? AND HOW DO WE DO THE CALCULATION?

  • The Arrhenius equation quantitatively describes the relationship between the rate constant k, temperature and the activation energy. The rate constant value increases with increase in temperature and nothing else varies it!

    • k = A exp(–Ea/RT) 

      • k = rate constant (from the rate expression) e.g. rate = k [A]a [B]b etc.

      • A = a constant for a given reaction, sometimes called the 'frequency' or 'pre–exponential' factor and it seems to be linked to stereochemical factors i.e. the spatial aspects of a reactant particle collision.

      • Ea = activation energy in Jmol–1 

      • R = ideal gas constant = 8.314 Jmol–1K–1 

      • T = temperature in K (Kelvin = oC + 273)

  • Rewriting the Arrhenius equation in logarithmic form gives:

    • ln(k) = ln(A) – Ea/(RT)

    • or log10(k) = log10(A) – Ea/(2.303RT)

  • From accurate rate data at different temperatures (e.g. 5 or 10o intervals and a minimum of four results) you can calculate the values of k OR more simply, for a fixed 'recipe', a set of 'rate' results.

  • You then plot  the value of ln(k or relative rate) versus the reciprocal temperature in Kelvin. 

  • Table of some rate data for the reaction between hydrogen and iodine

  • Temp./K 1/T k ln(k)
    556 0.001799 0.0000445 -10.02
    575 0.001739 0.0001370 -8.896
    629 0.001589 0.0025200 -5.983
    666 0.001502 0.0014100 -4.262
    700 0.001429 0.0643000 -2.744

doc b

  • The negative gradient of the graph is equal to –Ea/R,

  • so, Ea = –R x gradient (in J, and /1000 => kJ).

    • In terms of y = mx + c, m = gradient = dy/dx = Ea/R, c = a constant = ln(A),

    • so, in terms of the Arrhenius equation, the algebra equates to

    • ln(k) = – Ea/(RT) + ln(A)

  • Example calculation for 6.1 to determine the activation energy of a chemical reaction

    • Some accurate rate constant data for various temperatures are tabulated above for the reaction between hydrogen and iodine to form hydrogen iodide.

    • H2(g) + I2(g) ==> 2HI(g)

    • rate = k2 [H2(g)] [I2(g)]

    • The Excel Arrhenius plot of ln(k) versus 1/T ...

    • The Excel plot routine conveniently provided the best line fit.

    • y = –19867 + 25.651

    • therefore gradient = –19867 = –Ea/R

    • so, Ea = 19867 x 8.314 = 165174 J mol–1,

    • activation energy, Ea = 165 kJ mol–1 (3 sf, 165.2 4sf)

    • The constant A can be calculated as follows:

    • The constant 25.651 = ln(A), therefore A = e25.651 , so A = 1.325 x 1011,

    • so the full Arrhenius expression for the hydrogen iodine reaction is

    • k = Ae(Ea/RT) = 1.325 x 1011 x e(165174/8.314T)


Advanced A Level Kinetics Index

Revision notes for GCE Advanced Subsidiary Level AS Advanced Level A2 IB Revise AQA GCE Chemistry OCR GCE Chemistry Edexcel GCE Chemistry Salters Chemistry CIE Chemistry, WJEC GCE AS A2 Chemistry, CCEA/CEA GCE AS A2 Chemistry revising courses for pre–university students (equal to US grade 11 and grade 12 and AP Honours/honors level courses) kinetics * 5. Arrhenius equation for calculating activation energy

KS3 BIOLOGY QUIZZES ~US grades 6-8 KS3 CHEMISTRY QUIZZES ~US grades 6-8 KS3 PHYSICS QUIZZES ~US grades 6-8 HOMEPAGE of Doc Brown's Science Website EMAIL Doc Brown's Science Website
GCSE 9-1 BIOLOGY NOTES GCSE 9-1 CHEMISTRY NOTES and QUIZZES GCSE 9-1 PHYSICS NOTES GCSE 9-1 SCIENCES syllabus-specification help links for biology chemistry physics courses IGCSE & O Level SCIENCES syllabus-specification help links for biology chemistry physics courses
Advanced A/AS Level ORGANIC Chemistry Revision Notes US K12 ~grades 11-12 Advanced A/AS Level INORGANIC Chemistry Revision Notes US K12 ~grades 11-12 Advanced A/AS Level PHYSICAL-THEORETICAL Chemistry Revision Notes US K12 ~grades 11-12 Advanced A/AS Level CHEMISTRY syllabus-specificatio HELP LINKS of my site Doc Brown's Travel Pictures
Website content © Dr Phil Brown 2000+. All copyrights reserved on revision notes, images, quizzes, worksheets etc. Copying of website material is NOT permitted. Exam revision summaries & references to science course specifications are unofficial.

Advanced A Level Kinetics Index

 Doc Brown's Chemistry 

*

best gift deals latest video game release, best gift deals best bargains in shop sales latest pop music releases, best sales deals download free music, latest film releases, best gifts for teenagers latest high street fashion in clothes, fashionable trending in clothing, best gift deals best bargains in shop salesgirls buy clothes, spend a lot of money on clothes, best sales deals shoes, sweets and chocolates, magazines and make-up best gifts for teenagers Boys buy food and drink, computer games best gift deals best bargains in trainers shop sales DVDs and CDs, girls and boys spend a lot of money on credit for mobile phones best sales deals best bargains in shop sales buses and trains to transport them going out best gifts for teenagers best bargains in shoes shop sales Girls spend a lot of money on clothes best gift deals color colour preferences in clothes, cool sunglasses best sales deals boys buy expensive thins like best gifts for teenagers designer sports clothes and trainers, teenagers save for holidays, best sales deals clothes, mobile phones, birthday presents and electronic goods, teenage accessories, Favourite style of jeans. best gifts for teenagers A typical girl’s shopping list includes mobile phone credit deals best shoes gift deals fashionable quality cool airpods, air pods, fashionable clothes best sales deals the most popular favourite sneakers best gifts for teenagers fancy shoes, sweets, chocolates, magazines, best trainers gift deals best bargains in shop sales lip moisturizer best bargains in  shop sale slots on make-up, well being, teenage decor decorating their room best sales deals teenagers like LED string lantern lights, best gifts for teenagers beauty products for teenagers, denim jackets, scrunchies coolness, fashionable back packs, typical boy’s shopping list includes mobile credit deals, eating out takeaway food and drinks, what teenagers like to buy in clothes best gifts for teenagers computer games, DVDs, CDs, what teenagers talk about best gift deals what teenagers worry about, what teenagers like to do for fun sports best sales deals what cool things do teenagers buy, resale websites like eBay Teenager best high street shop or best online deals currys pc world argos amazon john lewis dell acer samsung raycon bose sony asus huawei HP microsoft in-ear headphones earbuds ipad desktop computer laptop computer for school college university students latest video games consoles apple iphone google high end mobile phones cell phone bargain smartphone xiaomi oppo high tech products latest fashion in trainers latest fashion in shoes latest fashion in mobile phones cell phones

TOP OF PAGE