What is the change in enthalpy for the final reaction?
Eq. 1 2Zn(s)+O_2(g)rarr2ZnO(s) DeltaH=-696.0 kJ/mol
Eq. 2 O_2(g)+2H_2(g)rarr2H_2O(l) DeltaH=-571.6 kJ/mol
Eq. 3 Zn(s)+2HCl(g)rarrZnCl_2(s)+H_2(g) DeltaH=-231.29 kJ/mol
ZnO(s)+2HCl(g)rarrZnCl_2(s)+H_2O(l)
Eq. 1
Eq. 2
Eq. 3
1 Answer
Explanation:
Your goal here is to rearrange the thermochemical equations given to you in order to find a way to get to the target reaction
"ZnO"_ ((s)) + 2"HCl"_ ((g)) -> "ZnCl"_ (2(s)) + "H"_ 2"O"_ ((l))
You know that you have
2"Zn"_ ((s)) + "O"_ (2(g)) -> 2"ZnO"_ ((s))" " DeltaH = - "696.0 kJ mol"^(-1)" "color(blue)((1))
"O"_ (2(g)) + 2"H"_ (2(g)) -> 2"H"_ 2"O"_ ((l))" "DeltaH = - "571.6 kJ mol"^(-1)" "color(blue)((2))
"Zn"_ ((s)) + 2"HCl"_ ((g)) -> "ZnCl"_ (2(s)) + "H"_ (2(g))" "DeltaH = - "231.29 kJ mol"^(-1)" "color(blue)((3))
Now, the first thing to notice is that the target reaction has zinc oxide as a reactant, so reverse equation
2"ZnO"_ ((s)) -> 2"Zn"_ ((s)) + "O"_ (2(g))" "color(blue)((1^'))
As you know, when you reverse a chemical reaction, you change the sign of its enthalpy change of reaction. This means that for equation
DeltaH_ (1^') = + "696.0 kJ mol"^(-1)
Next, divide all the coefficients in reaction
"ZnO"_ ((s)) -> "Zn"_ ((s)) + 1/2"O"_ (2(g))" "color(blue)((1^''))
After doing this, you need to divide the value of the enthalpy change of reaction by
DeltaH_ (1^'') = + "348.0 kJ mol"^(-1)
Next, divide all the coefficients in reaction
1/2"O"_ (2(g)) + "H"_ (2(g)) -> "H"_ 2"O"_ ((l))" "color(blue)((2^'))
Remember to divide the enthalpy change of reaction by
DeltaH_ (2^') = - "285.8 kJ mol"^(-1)
You are now ready to add equations
color(white)(aaaaaaaaa)"ZnO"_ ((s)) -> color(purple)(cancel(color(black)("Zn"_ ((s))))) + color(red)(cancel(color(black)(1/2"O"_ (2(g))))) " " " " " " +
color(white)()color(red)(cancel(color(black)(1/2"O"_ (2(g))))) + color(green)(cancel(color(black)("H"_ (2(g))))) -> "H"_ 2"O"_ ((l))
color(purple)(cancel(color(black)("Zn"_ ((s))))) + 2"HCl"_ ((g)) -> "ZnCl"_ (2(s)) + color(green)(cancel(color(black)("H"_ (2(g)))))
color(white)(aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa)/color(white)(a)
"ZnO"_ ((s)) + 2"HCl"_ ((g)) -> "ZnCl"_ (2(s)) + "H"_ 2"O"_ ((l))
To find the enthalpy change of reaction, simply add the enthalpy changes of reaction that correspond to equations
You will have
DeltaH_"target" = +"348.0 kJ mol"^(-1) + (-"285.8 kJ mol"^(-1)) + (-"231.29 kJ mol"^(-1))
DeltaH_"target" = color(darkgreen)(ul(color(black)(-"169.1 kJ mol"^(-1))))
The answer is rounded to one decimal place.
