A2.747g sample of manganese metal is reacted with excess hcl gas to produce 3.22l hydrogen gass at 373 k and 0.951 atm and a manganese chloride compound (mnclx). determine the formula of the manganese chloride produced by this reaction.

1. Find moles! In this case, since we are dealing with H2 gas, we will be using PV=nRT (Where P is pressure, V is volume in liters, n is moles, R is the gas constant specific for the pressure unit and T is temp in Kelvin).
(0.951 atm)(3.22L)=n(.082057)(373K)  
3.062=30.607n  n=0.100 moles H2

Mn (s) +HCl (g)-->  H2 (g)+ Mn(Cl#)

The ratio of HCl to H2 must be 2:1 (Although we do not know the exact number, the ratio must be that so the actual equation can be balanced)
0.100 moles H2* (2 mol HCl/1molH2)=0.200 moles HCl 
0.200 moles HCl * (1mol Cl-/1molHCl)=0.200 moles of chlorine 
2. Find moles of manganese
2.747g Mn * (1 mol Mn/54.938g Mn)=0.05000 moles Mn

3. Mole Ratio
0.05000 moles Mn/0.200 moles chlorine=0.25 (A ratio of 1/4)
The formula should be MnCl₄

Yes, endothermic means it turns cold. and some chemical changes include change of tempature.