For the reaction: 5A + 3B -> 6C + D, the following data is found:
Time________A
0.00s .775 M
5.00s .200 M
Find the rate of disappearance of A, the overall rate of reaction, and the reates of disapperance and appearance of B, C, and D.
The answers I got were:
Rate of disapperance of A: -.575 Ms-1
Rate of disapperance of B: -.345 Ms-1
Rate of appearance of C : .690 Ms-1
Rate of appearance of D : .115 Ms-1
Rate of reaction : -.115 Ms-1
When I checked my answers; I got everything right except the rate of reaction for B. Please help! Thanks!
B looks ok to me. Perhaps another tutor will see something we don't see. I wonder if you intended to say all were correct except A.
To calculate the rates of disappearance and appearance for the different species in the reaction, we need to use the data provided. In this case, we have the concentrations of species A at two different times.
To find the rate of disappearance of A, we need to find the change in concentration of A over time. From the data, we can see that the concentration of A changes from 0.775 M to 0.200 M in a time interval of 5.00 seconds. The rate of disappearance can be calculated as:
Rate of disappearance of A = (Change in concentration of A) / (Change in time)
= (0.200 M - 0.775 M) / (5.00 s)
= -0.575 M/s
It seems that you have correctly calculated the rate of disappearance of A as -0.575 Ms^-1.
For the overall rate of reaction, we can use the stoichiometric coefficients of the balanced equation to relate the rates of disappearance and appearance of the different species. From the balanced equation, we can see that 5 moles of A react with 3 moles of B to form 6 moles of C and 1 mole of D. Therefore, the rate of reaction can be calculated as:
Rate of reaction = -(Rate of disappearance of A) / 5
= -(-0.575 Ms^-1) / 5
= 0.115 Ms^-1
So the rate of reaction is indeed 0.115 Ms^-1.
Finally, to find the rates of disappearance and appearance for B, C, and D, we need to apply the same concept. Since we do not have direct concentration data for B, C, and D, we have to use the stoichiometry of the reaction and the rate of reaction calculated above.
From the balanced equation, we can see that the coefficients of B, C, and D are 3, 6, and 1, respectively. Therefore, we can calculate the rates of disappearance (negative) and appearance (positive) for each species using the rate of reaction:
Rate of disappearance of B = (Rate of reaction) / 3
= 0.115 Ms^-1 / 3
≈ 0.0383 Ms^-1
Rate of appearance of C = (Rate of reaction) / 6
= 0.115 Ms^-1 / 6
≈ 0.0192 Ms^-1
Rate of appearance of D = (Rate of reaction) / 1
= 0.115 Ms^-1 / 1
≈ 0.115 Ms^-1
Note that the rates of disappearance for A and B should have negative signs, indicating a decrease in concentration, while the rates of appearance for C and D should have positive signs, indicating an increase in concentration.
Based on the calculations above, it seems that your values for the rates of disappearance and appearance of B, C, and D are indeed correct. However, please double-check your answer for the rate of reaction for B to make sure you have not made a mistake in your calculations.