# substance

1. ### Equation for chemical potential of pure substance. Unsure why this derives as it does

Hello, I am new to this. I have attached a screenshot from a journal article which talks about deriving Fick's first law. My calculus is a little rusty, and I don't understand how equation 5 is derived from equation 4. I'd have a go, but I have little to offer. All I have to offer is...
2. ### Defining substance

I’m fairly new to the world of physics but am extremely intrigued by many of its various fields. Most recently I have been struggling to find a clear answer as to what determines if something has substance. My novice assumption would be that substance can be defined by its interaction with...
3. ### Half life of substance

cancer a patient who is undergoing cancer theraphy is given 10 mins of irradiation from a radioactive source that has half life = 2 years. If the same source is to be used for same treatment 2 years later , how long should the patient should be irradiated? the ans is 20 mins .. can someoene...
4. ### Calculate the net charge on a substance consisting of a combination of 7.8 1013 prot

Calculate the net charge on a substance consisting of a combination of 7.8 1013 protons and 3.0 1013 electrons.