Can you have an endothermic reaction when H>0?

Which of the following is always a reactant in a combustion reaction? oxygen nitrogen hydrogen carbon

This chart lists four kinds of polymers and their sources. what can be known about all four polymers, despite their differences? they come from living things. they share ionic carbon bonds. they are at least 100 monomers long. they are made of repeating subunits.

Based on its chemical properties, identify the position of each chemical family on the periodic table.