You have a stock solution of hno3 with a concentration of 4.5x10-4 m. however, you need 275 ml of a 2.50x10-5 m solution. how much of the stock solution will you need?

27.5 mL.

Explanation:

We have the rule that the no. of millimoles of the solution before dilution is equal to the no. of millimoles after dilution.

(MV)before dilution = (MV)after dilution,

M before dilution = 4.5 x 10⁻⁴ M, V before dilution = ??? mL,

M after dilution = 2.50 x 10⁻⁵ M, V after dilution = 275.0 mL.

∴ V before dilution = (MV)after dilution / M before dilution = (2.50 x 10⁻⁵ M)(275.0 mL) / (2.50 x 10⁻⁵ M) = 27.5 mL.

"standard molar enthalpy:

h2o ( liquid water ) : - 285.8 kj/mole

h2o ( water vapor ) : - 241.8 kj / mole.

δhrxn = - 241. 8 - ( - 285.8 )= -241.8 + 285.8 = 44.0

answer: 44.0 kj"

the answers would be

the first one and the second one