Explanation:
Pure subsance is a substance that is made up of only one type of particle - each piece is the same throughout.
Being present before the reaction but not after means it's no the same (it couldve evaporated)
Answer: B
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Answer:
The standard enthalpy of combustion of solid urea ((CO(NH2)2) is -632 kJ mol-1 at 298 K and its standard molar entropy is 104.60 J K-1 mol-1
Explanation:
Answer:
D. 18.7 grams
Explanation:
The coefficients are the key.
Create a proportion with them, and the molar mass, and then solve for x:

90 grams due to laws of conservation of mass. Output mass = input mass. Mass can never be created or destroyed.