dat destroyer chem question on rate laws

[spoog74]

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2011 edition question #68 asks

Rate = k [A]^2^3


They ask what the possible units for k are...

The answer says to just add the exponents but then gives an answer of m ^-4 sec -1 , although if you add the exponents it should give you ^5

 

[Cool Beans]

If you rearrange and solve for k: k=Rate/([A]^2)(^3)
Rate is measured in M/s or (M)(s^-1)
substituting in units: k=(M)(s^-1)/(M^5)
k=(M^-4)(s^-1)

So you'll always have an s^-1 from the units of Rate, but depending on the overall rxn order the power for molarity will vary. The shortcut being referenced here is that if you add the absolute values of the powers for molarity and seconds, then it coincidentally will equal the overall rxn order (which is 5 in your example).

 

[RCLEE]

2011 edition question #68 asks

Rate = k [A]^2^3


They ask what the possible units for k are...

The answer says to just add the exponents but then gives an answer of m ^-4 sec -1 , although if you add the exponents it should give you ^5

The answer is right. That's just the weird thing about rate order units. I think in the explanation has all of the units for the reaction orders.