Why do some surface apply more friction on a rolling object that others do

What are the spectator ions in 2h+ + so42- + ca2+ + 2r → caso4 + 2h+ + 21?

Which statement is usually true about the relationship between activation energy and reaction rates? low activation energy barriers result in low rates. high activation energy barriers result in low rates. low activation energy barriers result in no reaction. high activation energy barriers result in no reaction.

What is the ph of a solution that has a hydrogen ion concentration of 1.0 * 10 -9 m?