Label each of the following reactions as exothermic or endothermic ("exo" or "endo"), and according to whether work is done on or by the system, or no work is done at all ("on", "by" or "none")? Note that no "endo-on" cases appear here, as these are always thermodynamically unfavourable. There is no need to do any calculation, use chemical arguments to predict the sign of the enthalpy change.
Matching pairs
N2(l) --> N2(g)
Cl2(aq) + 2 KBr(aq) --> 2 KCl(aq) + Br2(aq)
Zn(s) + 2HCl(aq) --> ZnCl2(aq) + H2(g)
NH3(g) + HCl(g) --> NH4Cl(s)
S(s) + 3/2 O2(g) --> SO3(g)
nvm, i did some reworking
heres what my final answer
endo-by
exo-none
exo-by
exo-on
exo-on
can someone confirm please?
Umm this question is on our Quiz 5 ... anyways I don't understand the concept really i understand that when you are breaking bonds you need energy and when you making bonds you release energy ... and for work I think you need to look at the volume gas yet I am not sure about that part :(
for first question : exothermic you need energy to break bonds and form gasous forms and so on ... yet i don't know about the work part
yes.. i got the same answer :)
To determine whether a reaction is exothermic or endothermic, we need to look at the change in enthalpy (ΔH) for that reaction. Enthalpy is a measure of the heat energy associated with a reaction.
If the ΔH value is negative, the reaction is considered exothermic, meaning it releases heat to the surroundings. If the ΔH value is positive, the reaction is considered endothermic, meaning it absorbs heat from the surroundings.
In terms of whether work is done on or by the system, or no work is done at all, we need to consider the presence of pressure-volume work in the reaction. If there is a change in volume, work is being done on or by the system. If there is no change in volume, then no work is done.
Let's examine each reaction:
1. N2(l) --> N2(g)
- This reaction involves the evaporation of liquid nitrogen into gaseous nitrogen. Since this phase change involves breaking intermolecular forces, it requires energy input. Thus, it is an endothermic reaction (ΔH > 0). Additionally, since there is a change in volume (liquid to gas), work is done by the system (work is done on the surroundings). Therefore, we can label this reaction as endo-by.
2. Cl2(aq) + 2 KBr(aq) --> 2 KCl(aq) + Br2(aq)
- This reaction involves the combination of chlorine gas with potassium bromide in an aqueous solution, resulting in the formation of potassium chloride and bromine. To determine whether this reaction is exothermic or endothermic, we would need to know the ΔH value. However, it is mentioned that no calculations are needed, so we cannot determine the exact exothermic or endothermic nature of this reaction. However, by looking at the stoichiometry of the reaction, we can infer that it requires energy input to break the bonds in chlorine gas and potassium bromide, suggesting an endothermic reaction (ΔH > 0). In terms of work done, there is no change in volume, so no work is done (none). Therefore, we can label this reaction as endo-none.
3. Zn(s) + 2HCl(aq) --> ZnCl2(aq) + H2(g)
- This reaction involves the reaction between solid zinc and hydrochloric acid to produce aqueous zinc chloride and hydrogen gas. Metal displacement reactions like this typically release energy as the metal replaces hydrogen. Thus, it is an exothermic reaction (ΔH < 0). Again, since there is a change in volume (gas is produced), work is done by the system (work is done on the surroundings). Therefore, we can label this reaction as exo-by.
4. NH3(g) + HCl(g) --> NH4Cl(s)
- This reaction involves the combination of gaseous ammonia and gaseous hydrogen chloride to form solid ammonium chloride. This reaction is exothermic as energy is released when the ionic compound is formed (ΔH < 0). Since there is no change in volume, no work is done (none). Therefore, we can label this reaction as exo-none.
5. S(s) + 3/2 O2(g) --> SO3(g)
- This reaction involves the combination of solid sulfur with gaseous oxygen to produce gaseous sulfur trioxide. The formation of SO3 is exothermic as energy is released during the reaction (ΔH < 0). Since there is a change in volume (as gas is produced), work is done by the system (work is done on the surroundings). Therefore, we can label this reaction as exo-by.
In summary, the labeled reactions are:
1. N2(l) --> N2(g): endo-by
2. Cl2(aq) + 2 KBr(aq) --> 2 KCl(aq) + Br2(aq): endo-none
3. Zn(s) + 2HCl(aq) --> ZnCl2(aq) + H2(g): exo-by
4. NH3(g) + HCl(g) --> NH4Cl(s): exo-none
5. S(s) + 3/2 O2(g) --> SO3(g): exo-by
Okay, so basically i think i got all the endo and exo figured out because of either state change (heat released or used) but how do i figure out the "on", "by" or 'none' part?
1) exo
2)exo
3)endo
4)exo
5)exo