Cho các phương trình nhiệt hóa học sau:

Cho các phương trình nhiệt hóa học sau:

\begin{array}{l}\left(\text{1}\right)\text{C}\text{S}{}_{\text{2}}(l)\text{+}\text{3}\text{O}{}_{\text{2}}(g)\underset{}{\overset{t^o}{\to }}\text{C}\text{O}{}_{\text{2}}(g)\text{+}\text{2}\text{S}\text{O}{}_{\text{2}}\left(g\right) {\Delta }_{\text{r}}{\text{H}}_{298}^0\text{=}\text{–}\text{1}\text{1}\text{1}\text{0}\text{,}\text{2}\text{1}\text{k}\text{J}\\ \left(\text{2}\right)\text{C}\text{O}{}_{\text{2}}(g)\stackrel{}{\to }\text{C}\text{O}(g)\text{+}\text{1}\text{/}\text{2}\text{O}{}_{\text{2}}\left(g\right) {\Delta }_{\text{r}}{\text{H}}_{298}^0\text{=}\text{+}\text{2}\text{8}\text{0}\text{,}\text{0}\text{0}\text{k}\text{J}\\ \left(\text{3}\right)\text{N}\text{a}(s)\text{+}\text{2}\text{H}{}_{\text{2}}\text{O}(l) \stackrel{}{\to }\text{N}\text{a}\text{O}\text{H}(aq)\text{+}\text{H}{}_{\text{2}}\left(g\right) {\Delta }_{\text{r}}{\text{H}}_{298}^0\text{=}\text{–}\text{3}\text{6}\text{7}\text{,}\text{5}\text{0}\text{k}\text{J}\\ \left(\text{4}\right)\text{Z}\text{n}\text{S}\text{O}{}_{\text{4}}(s)\stackrel{}{\to }\text{Z}\text{n}\text{O}(s)\text{+}\text{S}\text{O}{}_{\text{3}}\left(g\right) {\Delta }_{\text{r}}{\text{H}}_{298}^0\text{=}\text{+}\text{2}\text{3}\text{5}\text{,}\text{2}\text{1}\text{k}\text{J}\end{array}

Trong các phương trình nhiệt hóa học trên, có bao nhiêu phản ứng thu nhiệt?

Đáp án: __