A mixture of ideal gases has the following composition by mass:

If the universal gas constant is $$8314$$ $$J/kmol$$-$$K,$$ the characteristic gas constant of the mixture (in $$J/kg$$-$$K$$) is ____________.

One side of a wall is maintained at $$400K$$ and the other at $$300K.$$ The rate of heat transfer through the wall is $$1000W$$ and the surrounding temperature is $${25^ \circ }C.$$ Assuming no generation of heat within the wall, the irreversibility (in $$W$$) due to heat transfer through the wall is ____________