Final answer:
Cyanide blocks cytochrome c oxidase, halting the electron transport chain and preventing ATP generation, leading to a decrease in pH of the intermembrane space.
Step-by-step explanation:
When cyanide poisoning occurs, it inhibits cytochrome c oxidase, a crucial component of the electron transport chain (ETC). As a consequence, the movement of electrons through the ETC halts, preventing the creation of the proton gradient that powers ATP synthase. Without ATP synthase functioning to generate ATP, the intermembrane space's proton concentration would increase—thus we would expect the pH to decrease.
Cyanide's effect on ATP synthesis would be devastating: it stops the production of the vast majority of ATP that would typically be generated from glucose, meaning that instead of up to 34 ATP molecules being made per glucose molecule through oxidative phosphorylation, significantly fewer will be produced, severely affecting cellular energy levels.