Why is My Second-Order Reaction Rate Calculation Incorrect?

• Chemistry
• guiromero
In summary, the user has a doubt about the rate of reaction and tries to find the answer using the reaction scheme, but gets an incorrect result.
guiromero
Homework Statement
Butadiene can be react with itself to form a dimer molecule. The reaction is second order in butadiene. The value of the rate constant is 7.7 x 10-3 M-1 s-1.

What is the initial rate consumption of butadiene in a reactor filled with butadiene to a concentration of 3.091 M? Express your answer in M/s.
Relevant Equations
r = k*C^2
Hello,

I have a doubt in an exercise about rate of reaction. The statement is quoted above and the reaction scheme is the following:

As the reaction is second order, I tried to apply the formula r = k*C^2.

Where r = rate of reaction
k = rate constant
C = concentration

So, I got:
r = (7.7e-3)*(3,091)^2 = 0,073 M

However, this not correct. I know it because when I click the "Send answer" button, it says "incorrect". Furthermore, the "Show answer" button doesn't display the answer.

Could anyone give some help?

Thanks a lot.

guiromero said:
So, I got:
r = (7.7e-3)*(3,091)^2 = 0,073 M
Is this result properly rounded? (Also, careful with the units.)

I tried to round from 0.07 to 0.075 and it didn't work.
The units are ok, as k[M^-1*s^-1] * C^2[M^2] = r[M * s^-1]

guiromero said:
I tried to round from 0.07 to 0.075 and it didn't work.
In my calculator,
$$7.7 \times 10^{-3} (3.091)^2 = 0.073567963$$
which, rounding to two significant figures, should give 0.074. You might try also 0.0736 or 0.07357 in case the preprogrammed solution was entered with an incorrect number of significant figures.

guiromero said:
The units are ok, as k[M^-1*s^-1] * C^2[M^2] = r[M * s^-1]
It's just that you wrote the units as M instead of M/s in the OP.

DrClaude said:
In my calculator,
$$7.7 \times 10^{-3} (3.091)^2 = 0.073567963$$
which, rounding to two significant figures, should give 0.074. You might try also 0.0736 or 0.07357 in case the preprogrammed solution was entered with an incorrect number of significant figures.It's just that you wrote the units as M instead of M/s in the OP.
I tried the values that you mentioned but it didn't work.
I think what you trying to say is the units of rate. I put M*s^-1 for M/s. I don't know if this is what you mean.

guiromero said:
So, I got:
r = (7.7e-3)*(3,091)^2 = 0,073 M
You wrote M instead of M s-1.

berkeman
DrClaude said:
You wrote M instead of M s-1.
Oh yes, thanks.

What is the consumption rate of a reactant?

The consumption rate of a reactant refers to the speed at which a reactant is used up in a chemical reaction. It is typically measured in terms of concentration change per unit time, such as moles per liter per second (M/s).

How is the consumption rate of a reactant calculated?

The consumption rate of a reactant is calculated by measuring the change in concentration of the reactant over a specified time period. Mathematically, it can be expressed as the negative change in concentration divided by the change in time: Rate = -Δ[Reactant]/Δt.

What factors affect the consumption rate of a reactant?

Several factors can affect the consumption rate of a reactant, including temperature, concentration of reactants, presence of a catalyst, and the physical state of the reactants (e.g., gas, liquid, or solid). Higher temperatures and concentrations generally increase the rate, while catalysts can lower the activation energy, speeding up the reaction.

Why is the consumption rate of a reactant important in chemical reactions?

The consumption rate of a reactant is important because it helps determine the speed and efficiency of a chemical reaction. Understanding this rate is crucial for optimizing industrial processes, controlling reaction conditions, and ensuring safety in chemical manufacturing.

Can the consumption rate of a reactant be constant throughout a reaction?

The consumption rate of a reactant is not usually constant throughout a reaction. It often changes as the reactant concentration decreases and products are formed. However, in zero-order reactions, the rate remains constant regardless of the concentration of the reactant.

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