In which of the following reactions is ΔE closest in value to ΔH?
HNO3(aq) + Na2(CO3)(aq) = NaNO3(aq) + H2O(l) + CO2(g)
KClO3(s) = KCl(s) + (3/2)O2(g)
HCl(aq) + NaOH(aq) = H2O(l) + NaCl(aq)
Na(s) + H2O(l) = NaOH(aq) + (1/2)H2(g)
dE = q+w so if w is zero dE = q. Which of those reactions produces the least work. Hint: Which reactions have a gas produced; which does not? A gas does work against the atmosphere when expanding.
To determine which of the given reactions has a ΔE closest in value to ΔH, we need to consider the nature of ΔE and ΔH and how they relate to each other.
ΔE represents the change in internal energy of a system, which includes both heat transfer (ΔH) and work done by or on the system. ΔH, on the other hand, represents the heat transfer at constant pressure.
In other words, ΔE = ΔH - PΔV, where PΔV is the work done by or on the system.
In reactions where the volume change is minimal or there is no significant work done, ΔE and ΔH can be considered approximately equal.
Let's analyze each reaction given:
1. HNO3(aq) + Na2(CO3)(aq) = NaNO3(aq) + H2O(l) + CO2(g)
This reaction involves the formation of a liquid (H2O) and a gas (CO2), which can result in a significant change in volume. Therefore, ΔE will not be equal to ΔH.
2. KClO3(s) = KCl(s) + (3/2)O2(g)
This reaction involves the conversion of a solid (KClO3) into a gas (O2), which results in a significant increase in volume. Again, ΔE will not be equal to ΔH.
3. HCl(aq) + NaOH(aq) = H2O(l) + NaCl(aq)
This reaction involves the formation of a liquid (H2O) and an aqueous solution (NaCl). Both are in the condensed phase, so there won't be a significant change in volume. Therefore, ΔE can be assumed to be close in value to ΔH.
4. Na(s) + H2O(l) = NaOH(aq) + (1/2)H2(g)
This reaction involves the formation of a gas (H2) and an aqueous solution (NaOH). It results in a significant increase in volume due to the formation of a gas phase. Therefore, ΔE will not be equal to ΔH.
Based on this analysis, the reaction where ΔE is closest in value to ΔH is:
HCl(aq) + NaOH(aq) = H2O(l) + NaCl(aq)