Dear johnLeong;
I assume, that with hr you are meaning hours!:
As all other units you are referencing don’t contain a time at all, there is no conversion possible!
kmole/hr is a rate, but in contrast mg/L or mg/kg are only concentrations.
Also mg/L is never equal mg/kg, except for very diluted solution in water!
But you are right that for the conversion from mole or kmole into grams or mg or kg the molecular weight of the compound is required.
Maybe you can explain more of your question, that we are able to help you.
Good Luck!
ARGOS++