The four statements below are used for applications of Hess's law. One of the statements is erroneous. Choose that statement.
a) the value of delta H for any reaction that can be written in steps is the sum of the values of delta H for each of the individual steps.
b) when an equation is reversed- written in the opposite direction- the sign of delta H must also be reversed (+ becomes - or - becomes +)
c) formulas cancelled from both sides of an equation must be for substances in identical physical states.
d) The value of delta H is independent of the stoichiometry, so that, if we change the equation, delta H does not change.
I chose d as the answer that is erroneous. Is this correct?
I agree.
Yes, your choice is correct. Statement d) is the erroneous statement.
Hess's law states that the overall enthalpy change of a reaction depends only on the initial and final states of the reaction and is independent of the pathway taken. This means that the value of ΔH is constant as long as the initial and final states of the reaction are the same, regardless of the stoichiometry or the specific steps taken to reach the final state.
For example, if a reaction can be written in multiple steps, the overall ΔH for the reaction is the sum of ΔH values for each individual step (statement a). If an equation is reversed, the sign of ΔH (enthalpy change) must also be reversed (statement b). If we cancel formulas from both sides of an equation, the substances must be in identical physical states (statement c).
However, statement d) is incorrect because the stoichiometry (ratios of reactants and products) of a reaction can indeed affect the value of ΔH. The enthalpy change is directly related to the amount of reactants and products involved in the reaction. So, if we change the stoichiometry of the equation, the value of ΔH will usually change as well.