To find the mass you you need multiply its volume by its density.
6 cm^3 • 2.76 g/cm^3 = 16.56 g
3.4 mol HCl * ( 36.46 g / 1 mol ) = 123.964 g HCl = 1.2 x 10^2 g HCl
Convert moles of HCl to grams of HCl using the molar mass ( 36.46 g/mol ).
Revise your answer to have the right number of significant figures ( 2 significant figures in this case, as determined by the the number of figures in the value with the least figures).
The color change would only effect the appearance of the substance, so it would be a physical change.
Answer: physical change
This is a missing part of your question:
The equilibrium system between sulfur dioxide gas, oxygen gas, and sulfur trioxide gas is given.
So you need the equilibrium balanced equation of SO2, O2, SO3 reaction:
First, we will start with the original equation which is not balanced yet (to understand how we get it):
SO2 + O2 ↔ SO3
Here the number of O atom is not equal at the to sides
So we will start to balance our equation by make the number of O atom equal each other on both sides:
So we will start to put 2SO3 instead of SO3
and put 2SO2 instead of SO2 to balance also the S atom on both sides
So we will get this:
2SO2(g) + O2(g) ↔ 2SO3(g) (This is our equilibrium balanced equation)
know we have a number of O atom equals on each side = 6
and the sulfur equals on each side = 2