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We have 3 modes of learning for students to choose from: weekly physical classes at Bishan; weekly online lessons via Zoom; and on-demand video lessons.

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Please be rest assured that I conduct all my classes personally and I do not engage other tutors to teach at my centre.

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Most of my students showed improvements by at least 3 grades and more than 80% have attained distinction for A Levels. The earlier the students join my classes, the more confident I am in improving their grades.

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Usually the class size is around 10 to 12 students. Max class size is 16 pax.

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Yes makeup lesson is available in the same week subject to availability. If makeup class is not possible, the student can view the recorded video lessons at Google Classroom.

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Yes we do. Fees for trial lesson are for Bishan class and for Zoom online class.

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Chemistry Guru specialises in H2 Chemistry for JC1 and JC2 or IP Year 5 and IP Year 6 students only. Find out all the information about A Level H2 Chemistry and the detailed comparison between H1 and H2 Chemistry. We do not conduct lessons for H1 Chemistry, O Level Chemistry, IB Chemistry or IP Chemistry at IP Year 3 and IP Year 4.

How to Draw Energy Cycle involving Enthalpy Change of Combustion - Energetics

In this video we want to learn how to draw the energy cycle given enthalpy changes of combustion of compounds and calculate the enthalpy change of a reaction using Hess' Law.

Let Chemistry Guru, Singapore's top JC Chemistry tuition centre, guide you through this exercise.

energy cycle enthalpy change combustion overall question

1. Draw Energy Cycle

First we have to write out the equation that represents enthalpy change of formation for propanol. Remember formation is forming 1 mole of a compound from its elements in their standard states.

energy cycle enthalpy change combustion formation of propanol

Since the products of combustion of carbon, H₂ gas and propanol are all CO₂ and H₂O, we can put them together at the bottom of the energy cycle and balance the equations.

For energy cycle involving combustion, we need to add O₂ gas to force out the combustion reactions so that we can make use of the enthalpy change of combustion for calculation.

energy cycle enthalpy change combustion balanced terms

Now we can add arrows for each combustion reaction.

First let's account for combustion of C₃H₈O. Enthalpy change of combustion is with respect to per mole of substance reacted with excess oxygen. Since coefficient of C₃H₈O is 1, enthalpy change of combustion for C₃H₈O remains as it is.

energy cycle enthalpy change combustion combustion of propanol

Next for combustion of C. Since coefficient of C is 3, enthalpy change of combustion for C has to be multiplied by 3.

energy cycle enthalpy change combustion combustion of carbon

Finally for combustion of H₂. Since coefficient of H₂ is 4, enthalpy change of combustion for H₂ has to be multiplied by 4.

energy cycle enthalpy change combustion combustion of hydrogen

2. Apply Hess' Law

Once the energy cycle is complete, we can determine which of these arrows are clockwise and counter-clockwise.

energy cycle enthalpy change combustion show direction of arrows

Finally we can apply Hess' Law by putting all the clockwise arrows on one side of the equation and all the counter-clockwise arrows on the other side of the equation to solve for the unknown enthalpy change.

energy cycle enthalpy change combustion hess law calculation