For each of the following gas-phase reactions, write the rate expression in terms of the appearance of each product and disappearance of each reactant:

(a) 2 H₂O(g) → 2 H₂(g) + O₂(g)

Video transcript

Welcome back everyone to another video, consider the gas phase reaction shown below. What is the rate expression in terms of the disappearance of the reactant and the formation of the products? We want to recall that we can define the rate of a specific reaction in terms of the rates of disappearance and appearance. We're going to start with our reactant and we know that reactants react, right, which means that their concentration is decreasing because that concentration is decreasing and the rate must be positive. We're including a negative sign for the rate of disappearance. Our next step is to include a fraction which will always have one in the numerator and the coefficient from the balanced equation in the denominator. So that'd be negative one half. And finally, we want to define the change in concentration of the reactant HF divided by the change and time. That's how we define the rate of disappearance of HF in relation to the rate of the reaction, we can now continue with our products. The first product of interest is age two. And now we're going to use a positive sign because we have a positive rate of appearance for our products. Now, the fraction that we're going to use is a one divided by one. Since the coefficient and the bounced equation is a one because one divided by one is simply one, we're going to exclude that number from our expression and simply write delta concentration of H two, meaning the change in concentration of hygiene divided by the change in time. And now we have fluorine F two, our final product. Therefore, we're going to use a positive sign change in the concentration of F two divided by the change in time. And now we have the expression that we need it. It relates the rates of appearance and the disappearance based on the give balance equation. Thank you for watching.