What is the new pressure of a gas at stp, if it is heated to 850k (assume the gas is in a rigid container)

   3.115 atm

Solution:
Firstly, the temperature and pressure at STP is 273 K and 1 atm respectively.

Now, the question mentions a change in temperature from 273 K to 850 K, which has resulted in a change in pressure from 1 atm. Based on this, it is evident that this question is based on Gay- Lussac's Gas Law which notes that an increase in temperature, causes an increase in pressure since the two are directly proportional (once volume remains constant). As such, we can find the new pressure by employing  Gay-Lussac's Equation : 
                                   P₁  ÷  T₁  =  P₂  ÷  T₂

Since the initial temperature (T₁) is 273 K, the final temperature is 850 K (T₂) and the initial pressure (P₁) is 1 atm, then we can substitute these into the equation to find the final pressure (P₂).   
         
             ⇒         (1 atm)  ÷  (273 K)  =  P₂  ÷  (850 K)
             
             ⇒                P₂  =  (0.00366 K · atm)   ×  850 K

             ⇒                P₂  = 3.115 atm

Thus the new pressure is 3.115 atm.

It's not the same dearthe first one is in grams per mole while the other is not