O Level Chemistry & IP Chemistry Notes by 10 Year Series Author - Chemistry Specialist

O Level Chemistry Made Easy

O Level Chemistry – Rate of Reaction Mini Series Part 1

Today during the intensive coaching of my student under the Final Leap Program, i noticed that many students are not very confident about question on Rate of Reaction (sometimes called Speed of Reaction).

So today, i am going to discuss on this “Must-Score” chapter in O Level Chemistry (same for IB and ICGSE syllabus). Perhaps, i will start a mini-Series on Rate of Reaction for your?quick?revision during this examination period

Different chemical reactions take place at different speeds.

The amount of reactants and products change during a chemical reaction.

We can measure the speed of reaction by measuring:
— how quickly a product is formed per unit time
— how quickly a reactant is used up per unit time

Speed of Reaction = (Change in Amount of Reactant/Product) / time taken

Or (for reaction that produces a Gas),

Speed of Reaction = (Change in Volume of Gas) / time taken

We often see questions in exams relating to RATE GRAPHS – A graph obtained by plotting some measurable quantity (e.g, volume of carbon dioxide produced or loss in mass of flask & contents in the reaction between limestone & hydrochloric acid) against time in order to find the rate of reaction.

Gradient of tangent to any point on the curve
–> Rate of Reaction at any instant

Steeper the gradient
–> faster the reaction

At start of reaction, graph is the steepest
–> Rate at the start of ANY reaction is always Fastest

As reaction progresses, gradient becomes gentler
–> Reaction is Slowing Down

After sometime, the graph levels off
–> point of leveling off signifies the End of Reaction

Let’s check out a question on Rate Graphs!

Question 1:



(Click to view clearer image)

PS: Try it out and remember to leave us your suggested answer in the “Leave A Reply” section below, so that others can come in and dicuss about the answer.

Related Articles:

Sean Chua
Many know me as the Ten Year Series book author for JC A-Level H2 Chemistry and O-Level Pure Chemistry. My 19+ years of coaching experience (since 1999) with more than 1500 students from 180+ JCs and Secondary Schools has allowed me to understand the true reasons why students are not able to perform well in Chemistry. Most importantly, my strength lies in using everyday analogies (even grandmothers can understand!) to simplify abstract concepts. Also, my teaching methodology has been designed to be fun, enjoyable and effective for my students. If you want to have an enjoyable time learning Chemistry and being motivated to excel in Chemistry, contact me today at 98287357

Share:

Reader Interactions

Comments

  1. It depends on the context of the question. For rate of reaction questions, the X-axis will usually be time. In an experiment, we always start the stopwatch at time = 0 second. As such, the X axis must start at zero point. For the Y-axis, it will be based on case-by-case basis. It depends on what you are measuring with respect to time. Hope that helps.

  3. the answer is ‘A’….i spoxe….cux the volume of carbon dioxide when halved is 43 cm cube……nd wen we look at the x-axis it is 0.95 minutes.

  4. i thought it was B. but then I realized that its A.
    since it says half the amount of Carbondioxide, initially, we should know the total amount of CO2 produced. and respectively, it was 90 cm3. half of it would be surely 45cm3.

    and when we see the corresponding x graph (time), it is 0.95 min. SO yah.. its A.

    i really like this site 😉 thank you mister!

  6. A,

    half the reaction means half the calcium carbonate to react and therefore half of 90 i-e 45 cm cube of CO2 is produced and so the corresponding time……………….. 🙂

  7. Hi Garrick,

    You are Spot On! Your approach is correct.

    Do continue to share your thoughts and answers with the readers in this chemistry blogsite.

  8. Hi YJ,

    This is a common error made by many students.

    Please note that Since half of the carbonate is used, total volume of CO2 produced will be halved.

    Answer should be A for this question.

    PS: Do note that the amount of CO2 produced is NOT proportional to the reaction time.

    Let me know if you have further questions.

  9. Hi Rija,

    Your concepts is correct. Since half of the carbonate is used, total volume of CO2 produced will be halved.

    Answer should be A. Seems like you made an error while reading off the axes of the graph.

    Hope this helps.

  10. I think it’s (A).

    Since 90 cm3 is the total volume of gas evolved, half of it would be 45 cm3, and reading from the graph, it is about 0.95 mins.

  11. Since calcium carbonate is the limiting reactant, if it is halved, the product which is carbon dioxide would be halved.
    Hence answer should be C.
    Am i correct?

  12. Its something like the total vol of CO2 was produced in 90 cm cube.so for half calcium carbonate will be 45.and at 45 cm cube the time consumed is almost 1.5.so the ans is B

Leave a Reply

Your email address will not be published. Required fields are marked *