Question

bisc161: energy, chemical reactions and enzymes
e. of the two lines on the graph, which of them represents the reaction in the presence of a catalyst? how do you know?
f. if your two reactants are h₂ and o₂, what does the catalyst do in terms of the formation of water?
g. what aspects of the reaction change when you add a catalyst? if the catalysis is heat, how does it do this? if the catalyst is an enzyme, how does an enzyme act as a catalyst?
h. what happens to the δg of a reaction when a catalyst is added?
i. from this graph, can you tell if this is an exergonic or endergonic reaction? if so, how?

Explanation:

e. The line with the lower activation - energy barrier represents the reaction in the presence of a catalyst. Catalysts lower the activation energy, increasing the reaction rate.
f. A catalyst in the reaction of H₂ and O₂ to form water lowers the activation energy, allowing the reaction to proceed more readily. It does not change the stoichiometry or the thermodynamics of the reaction, just speeds up the rate at which equilibrium is reached.
g. When a catalyst is added, the activation energy of the reaction decreases. If the catalyst is heat, it provides energy to the reactant molecules to overcome the activation - energy barrier. If the catalyst is an enzyme, it binds to the reactant (substrate) at its active site, forming an enzyme - substrate complex, which lowers the activation energy through induced fit and other interactions.
h. The ΔG (Gibbs free energy change) of a reaction does not change when a catalyst is added. Catalysts only affect the rate of the reaction by lowering the activation energy, not the overall thermodynamics of the reaction.
i. Without seeing the graph, if the products have lower free energy than the reactants, it is an exergonic reaction (ΔG < 0); if the products have higher free energy than the reactants, it is an endergonic reaction (ΔG>0). If the graph shows the progress of the reaction with energy levels of reactants and products, we can determine this by comparing their free - energy values.

Answer:

e. The line with lower activation energy represents the catalyzed reaction because catalysts lower activation energy.
f. It lowers the activation energy for the formation of water from H₂ and O₂, speeding up the reaction.
g. Activation energy decreases. Heat provides energy; enzymes bind to substrates to lower activation energy.
h. ΔG does not change as catalysts do not affect thermodynamics.
i. Compare free - energy of reactants and products on the graph. If products have lower free - energy, exergonic; if higher, endergonic.