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Kruka [31]
3 years ago
9

Chemical reactions occur when molecules or atoms collide so that the bonds between atoms break and new bonds form. breaking the

bonds of the reactants requires energy; whereas, bond formation releases energy. select the statements regarding energy changes during a reaction that are true.
Chemistry
1 answer:
katen-ka-za [31]3 years ago
8 0
If two substances react and the temperature of the mixture decreases, the reaction is endothermic<span>. If two substances react and the temperature of the mixture increases, the reaction is </span>exothermic<span>. A chemical reaction involves the </span>breaking<span> of bonds in the reactants and the forming of bonds in the products.</span>
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Answer:

ΔH  = - 272 kJ

Explanation:

We are going to use the fact that Hess law allows us to calculate the enthalpy change of a reaction no matter if the reaction takes place in one step or in several steps. To do this problem we wll add two times the first step to second step as follows:

N2(g) +         3H2(g) →          2NH3(g)                 ΔH=−92.kJ  Multiplying by 2:      

2N2(g) +       6H2(g) →          4NH3(g)                        ΔH=− 184 kK

plus

4NH3(g) +     5O2(g) →          4NO(g) +6H2O(g)        ΔH=−905.kJ

__________________________________________________

2N2(g) +   6H2(g) + 5O2(g)→  4NO(g)  + 6H2O(g)      ΔH = (-184 +(-905 )) kJ

                                                                                     ΔH =    -1089 kJ

Notice how the intermediate NH3 cancels out.

As we can see this equation is for the formation of 4 mol NO, and we are asked to calculate the ΔH  for the formation  of one mol NO:

-1089 kJ/4 mol NO  x 1 mol NO =  -272 kJ (rounded to nearest kJ)

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