# Writing rate of disappearance and rate of appearance using rate law [closed]

I have studied that rate of disappearance and rate of appearance is the change in concentration of reactants and products (respectively) with respect to time. Thus,

$$\text{ROD} = -\frac{\Delta c_R}{\Delta T}$$

and

$$\text{ROA} = \frac{\Delta c_P}{\Delta T}$$

and

$$\text{rate of reaction} = % % \frac{\text{ROD}} {\text{stoichiometric coefficient}} % % = \frac{\text{ROA}} {\text{stoichiometric coefficient} }$$

Then writing rate of reaction using rate law was taught.

And according to rate law rate of reaction can be expressed as:

$$\text{rate of reaction} = k[\ce{A}]^x[\ce{B}]^y$$

here $$x + y = \text{overall order of reaction}$$, with $$\ce{A}$$ and $$\ce{B}$$, the reactants.

Here is my confusion: Now they wrote rate of disappearance and appearance using rate law. How using rate law they wrote expression for ROA and ROD.

For a reaction: $$\ce{aA -> bB}$$ (elementary reaction), it was stated that: $$\text{ROD}_\text{A} = k_d [\ce{A}]^a$$

So how ?

Using rate law we can write rate of reaction.. (OK) but how can we write ROA and ROD ??!!

Hope you understood what I meant to say.

• How did you come to the last equation? Jan 11 at 19:59
• @PoutnikCan we relate rate law with ROD of reactant A as this formula : Rate of reaction = $-\frac{1}{Stoichiometric\space Coefficient\space of \space reactant A}\cdot\frac{\Delta[A]}{\Delta{t}} = k[A]^x[B]^y$ Jan 13 at 8:49
• @Poutnik I have made amendment to the reaction. Sorry for caused ambiguity. Now can you please explain how we can write ROD and ROA using RATE LAW ? Jan 13 at 11:24
• IF ROD(A)=ROR . SC and if ROR= k . [A]^x . [B]^y then ....... Jan 13 at 12:15