There's no set answer to how long the battery charge will last - it all depends on what you're doing with the tablet. Actions such as connecting to the internet, playing games or movies and other complex tasks will consume power faster than more simple tasks like writing emails or reading an ebook.
THE EFFECT OF CHANGING CONDITIONS IN ENZYME CATALYSIS This page looks at the effect of changing substrate concentration, temperature and pH on reactions involving enzymes. It follows on from a page describing in simple terms how enzymes function as catalysts.
Changes in pH may not only affect the shape of an enzyme but it may also change the shape or charge properties of the substrate so that either the substrate connot bind to the active site or it cannot undergo catalysis. In geneal enzyme have a pH optimum. However the optimum is not the same for each enzyme.