Atomic number of element is 15 while mass is 31 how many neutrons does the element have

What is the ph of a solution with a 1.50 × 10−9 m hydroxide ion concentration?

Think about how you can use le chatelier’s principle to find possible solutions to the design problem. describe at least two ways to increase the yield (amount) of ammonia based on this principle.

Two nitro no2 groups are chemically bonded to a patch of surface. they can't move to another location on the surface, but they can rotate (see sketch at right). it turns out that the amount of rotational kinetic energy each no2 group can have is required to be a multiple of ε, where =ε×1.010−24 j. in other words, each no2 group could have ε of rotational kinetic energy, or 2ε, or 3ε, and so forth — but it cannot have just any old amount of rotational kinetic energy. suppose the total rotational kinetic energy in this system is initially known to be 32ε. then, some heat is removed from the system, and the total rotational kinetic energy falls to 18ε. calculate the change in entropy. round your answer to 3 significant digits, and be sure it has the correct unit symbol.