How do I convert 25.0 kPa into mmHg? Also, how do I convert 1.17 atm into kPa?

Knowing the values of standard pressure in different units will help you do these conversions:

Standard pressure = 1.00 atm = 760 mmHg = 101.3 kPa

You can use the the ratio of pressures in two units as conversion factors:

25.0 kPa X (760 mmHg/101.3 kPa) = 188 mmHg

1.17 atm X (101.3 kPa/1.00 atm) = 119 kPa 

You can also find tables of pressure conversion factors by doing an Internet search. 

The S.I. unit for pressure is the Pascal (Pa), because one Pascal is equal to one Newton per square meter. The kilopascal (kPa) is used more commonly for atmospheric pressure because the size is more appropriate. The atmosphere is a convenient unit for measuring atmopheric pressure. It's the average pressure at sea level, so readings in atmospheres are easy to intepret.