Oxidation of glucose to carbon dioxide and water can occurs...

Oxidation of glucose to carbon dioxide and water can occur by combustion in the laboratory or by biological oxidation in living cells (see figure glucose degradation & synthesis in the slides). When combustion is carried out under controlled conditions, the reaction is highly exothermic, with an enthalpy change of -673 kcal/mol. The delta G for this reaction at 25°C is -686 kcal/mol, so the reaction is also highly exergonic. a) (0.25 points) Explain what the delta H and delta G values mean. What do the negative signs mean in each case? b) (0.25 points) Without doing any calculations, would you expect delta S for this reaction to be positive or negative? Explain. c) (0.25 points) Now calculate the delta S for this reaction at 25°C. Does the calculated value agree in sign with your prediction in part b? d) (0.25 points) What are the values of delta G, delta H, and delta S for the reverse reaction (synthesis of glucose)?

Transcript

00:01 Hello students in this question we have a reaction which is the combustion of glucose and glucose is c6 h12 06 and in combustion it reacts with oxygen to produce carbon dioxide water and energy so production of this energy it means that it is an exothermic reaction that is it releases energy at the product side.

00:33 Now, another information which are given to us is that the value of delta edge, that is change in enthalpy, which is equals to minus 673 kilo calorie per mole.

00:47 And we have delta g that is gibbs energy which is minus 686 kilo calorie per mole.

00:56 Now let's move towards the questions.

00:59 So we have first question.

01:02 It says that, it says that, what delta h and delta g means and what this negative sign sign signifies so delta h is the change in the energy of reaction which is nothing but total energy of product minus total energy of reactant this is delta h that is change in enthalpy now here if we have negative sign it means that we have energy of reactant more compared to energy of product so therefore we can write that energy of product is less than energy of reactant now let's look for delta g so delta g also known as gives energy and change in this energy if there is a reduction in this energy it shows the maximum possible work so so, it signifies maximum possible work that can be obtained from the system and that system is that on which we are doing the experiment.

02:50 Now, there is a huge significance of the sign convention of delta g.

02:55 If delta g is negative, it means that reaction is spontaneous.

03:00 Yes, it will happen itself.

03:03 It will not be requiring any external force for the reaction.

03:07 So it is a spontaneous reaction.

03:10 So here we have negative value.

03:11 It means it is a spontaneous reaction.

03:15 Now moving towards part b of the question.

03:21 So part b we have without doing any calculation, would you expect delta s for this reaction to be positive or negative? so yes we can predict the sign for delta s.

03:35 We know of formula that is delta g is equals to delta h minus t delta s.

03:42 So this is a thermodynamic formula where we have gibbs free energy as delta g, delta h is change in enthalpy, t is temperature and delta s is entropy.

03:54 So here t is temperature which is given to us as 25 degrees celsius and if we convert it into kelvin it is 298 kelvin.

04:05 So now we know the value of delta g it is more than delta h.

04:10 So it is negative.

04:13 Delta h is also negative...

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