Answer :
The question is incomplete. the complete question is:
A chemist measures the energy change during the following reaction: [tex]2NO_2(g)\rightarrow N_2O_4[/tex] [tex]\Delta H=-55.3kJ[/tex] 1. This reaction is:______. a. endothermic. b. exothermic.
2. Suppose 70.1 g of NO2 react. Will any heat be released or absorbed? A. Yes, absorbed. B. Yes, released. C. No.
3. If you said heat will be released or absorbed, calculate how much heat will be released or absorbed?
Answer:1. b. exothermic
2. Yes , released
3. 42.0 kJ
Explanation:
1. Endothermic reactions are those in which heat is absorbed by the system and exothermic reactions are those in which heat is released by the system.
[tex]\Delta H[/tex] for Endothermic reaction is positive and [tex]\Delta H[/tex] for Exothermic reaction is negative.
2. [tex]2NO_2(g)\rightarrow N_2O_4[/tex] [tex]\Delta H=-55.3kJ[/tex]
According to avogadro's law, 1 mole of every substance occupies 22.4 L at STP and contains avogadro's number [tex]6.023\times 10^{23}[/tex] of particles.
To calculate the moles, we use the equation:
[tex]\text{Number of moles}=\frac{\text{Given mass}}{\text {Molar mass}}=\frac{70.1g}{46g/mol}=1.52moles[/tex]
2 moles of [tex]NO_2[/tex] reacts, energy released = 55.3 kJ
1.52 moles of [tex]NO_2[/tex] reacts, energy released =[tex]\frac{55.3 kJ}{2}\times 1.52=42.0kJ[/tex]
Thus 42.0 kJ heat will be released when 70.1 g of [tex]NO_2[/tex] react.