Question

If the ΔH for H2O(l) → H2O(s) is -6.01 kJ, then what is the ΔH for 2H2O(s) → 2H2O(l)?

A. 12.02 kJ
B. 6.01 kJ
C. -12.02 kJ
D. -6.01 kJ

Answer 1

When a reaction is going in the opposite direction, the reaction changes from requiring heat to releasing heat or from releasing heat to requiring it. The negative on the change in enthalpy represents releasing heat, and a positive change in enthalpy represents requiring heat.
Also, if a reaction is multiplied by a constant, the change in enthalpy also must be multiplied by that constant.

Using this information, what do you think the answer is?

Answer 2

@JoannaBlackwelder C?

Answer 3

Close, that value would be for the reaction:
2H2O(l) → 2H2O(s)

Answer 4

so then A?

Answer 5

Notice that the reaction we are looking for is also reversed in direction, indicating that the change in enthalpy would need to change sign (indicate that it requires energy).

Answer 6

Right, A :-)

Answer 7

Thank you! :)

Answer 8

You're welcome :-)