# Kinetics

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#1
Hey

can someone explain to me how to work out the order of relation with respect to A and C? I know B is order one as you compare exp 1 and 2 (x4)
i get confused when two reactants change at the same time

thanks
0
5 years ago
#2
B is order 1 if you look at exp 1 and 2. Multiplying B by 4 multiplies the RR by 4.
A is order 2 because if you multiply A by two, the RR is multiplied by 4. For exp 1 and 3, B is multiplied by 8, so dividing the RR and B by 8, you see that dividing A by 2 divides the RR by 4.
For C look at exp 3 and 4. A is constant so can be ignored. B and C are variable. (0.3/0.8)=0.375
You can now multiply B in exp 3 by 0.375 and RR in exp 3 by 0.375, this gives
0.1, 0.30, 0.40, 0.6 x 10-3
From this you can work out the order with respect to C.
1
#3
(Original post by morgan8002)
B is order 1 if you look at exp 1 and 2. Multiplying B by 4 multiplies the RR by 4.
A is order 2 because if you multiply A by two, the RR is multiplied by 4. For exp 1 and 3, B is multiplied by 8, so dividing the RR and B by 8, you see that dividing A by 2 divides the RR by 4.
For C look at exp 3 and 4. A is constant so can be ignored. B and C are variable. (0.3/0.8)=0.375
You can now multiply B in exp 3 by 0.375 and RR in exp 3 by 0.375, this gives
0.1, 0.30, 0.40, 0.6 x 10-3
From this you can work out the order with respect to C.
Thank you! I've worked out that C has 0 order (?)
How do you know what is the constant? Is it always order 2?
0
5 years ago
#4
(Original post by Alltimesarah)
Thank you! I've worked out that C has 0 order (?)
How do you know what is the constant? Is it always order 2?
Yes I get A: 2, B: 1, C: 0.
The rate constant has order 0 because it is a constant.
The units of the rate constant are dm6mol-1s-1​.
0
5 years ago
#5
(Original post by morgan8002)
Yes I get A: 2, B: 1, C: 0.
The rate constant has order 0 because it is a constant.
The units of the rate constant are dm6mol-1s-1​.
The rate constant does not have an order, but if it did it would be 1 not 0 as any quantity raised to the power of 0 is 1 ...
0
5 years ago
#6
(Original post by charco)
The rate constant does not have an order, but if it did it would be 1 not 0 as any quantity raised to the power of 0 is 1 ...
Any constant has order 0. If it had order 1 that would imply that it changed with respect to another variable.
0
5 years ago
#7
(Original post by morgan8002)
Any constant has order 0. If it had order 1 that would imply that it changed with respect to another variable.
If a constant has order zero then it must equal 1.
0
5 years ago
#8
(Original post by charco)
If a constant has order zero then it must equal 1.
Consider a polynomial. x2 has order 2, x is order 1, 1 is order 0, x-1 has order -1 and so on.
Any constant can be considered a variable to the power of 0 multiplied by a coefficient.
It could not be order 1 as this would mean it changes as the variable changes, which would have significant consequences for the rate equation.

This is all assuming constant temperature.
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5 years ago
#9
(Original post by morgan8002)
Consider a polynomial. x2 has order 2, x is order 1, 1 is order 0, x-1 has order -1 and so on.
Any constant can be considered a variable to the power of 0 multiplied by a coefficient.
It could not be order 1 as this would mean it changes as the variable changes, which would have significant consequences for the rate equation.

This is all assuming constant temperature.
A variable to the power of 0 multiplied by a coefficient is just saying 1 x coefficient. The coefficient IS the constant!

It is meaningless to talk about order with respect to the rate constant.
0
5 years ago
#10
(Original post by charco)
A variable to the power of 0 multiplied by a coefficient is just saying 1 x coefficient. The coefficient IS the constant!

It is meaningless to talk about order with respect to the rate constant.
Any order n would mean that k = axn, where x is some variable. As the rate constant is always constant within the constraints of the question, n = 0, so the order is 0.

I think I see where you're coming from now. The order of the rate equation with respect to the rate constant is 1 but the order of the rate constant with respect to any other variable is 0. I think we were arguing over different things.

I do agree that it is pointless to talk about the order of the rate constant though.
0
5 years ago
#11
(Original post by morgan8002)
Any order n would mean that k = axn, where x is some variable. As the rate constant is always constant within the constraints of the question, n = 0, so the order is 0.

I think I see where you're coming from now. The order of the rate equation with respect to the rate constant is 1 but the order of the rate constant with respect to any other variable is 0. I think we were arguing over different things.

I do agree that it is pointless to talk about the order of the rate constant though.
0
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