Given the standard enthalpy changes for the following two reactions:

$(1)N_2(g)+O_2(g)2NO(g),H=181\mathrm{.}8kJ$

$(2)N_2(g)+2O_2(g)N_2{O}_4(g),H=9\mathrm{.}2kJ$

What is the standard enthalpy change for the following reaction?

$(3)2NO(g)+O_2(g)N_2{O}_4(g),H=$

Standard enthalpy change $=$ k$]$

$2$ item attempts remaining