Question

4. Hot packs. All reactions are spontaneous; note that some are exothermic and some are endothermic. How can a spontaneous reaction Increase in energy? Hot packs, exothermic: CaClas) → Calag) + 2CH(aq) 4,H=-81.35 kd/mol. MgSO4(s) → Mg?"(aq) +507(ag) AH-91.22 kJ/mol Just plain hot-watch out! NaOH(s) → Na'(aq) + OH'(aq) AH = -44.50 kJ/mol. a. Pick one of the above reactions and calculate how much 1.0 g of the solid would increase the temperature of 100 mL of water. Let your group mates do the other ones. b. Give a chemical explanation why these reactions are exothermic. Muster up your intuition and speculate why they are spontaneous.

Answer 1

Answers c (a). taking cacle(s) → cest (29.) + 2440 (aq.). 4H = - 81-35 kJ/mot i tühen 1 mol of cacla (s) dissolved in water il gives 81.35 KJ g energy. Molar mass of Calli = 40+(35.52) = 40 +?! = 111 g/mol. given mass of cacka = 19. '. number of motes = given mass ... 19 -= 0.009 Molar mass 111 g/mol mot. Now, I mot cach gives 81.38X103 J energy. 0.009 mot Cally given 81.35 X103x 0.009 I. = 732..15 J'energy. Now, specific heat of water is 4.186 5/9.0c - The energy required to increas temp.of 1g water by pe is 4.180 F . .; 1009 water require = 4:180 x 100 =418-J energy. Now, in reverse we can write. 4183 energy incremes temp. of 100g water by 1e. 2J i "onové °C. - 732.15 J".. ni n hil ex 732-15°C. = 1.75°C L

b) the reaction is exothermic because, the energy of product is less than energy of reactant. It goes from higher energy to lower energy, hence gives out the energy in the form of heat. This reaction i.e., exothermic reacton are spontaneous in nature because there is no need to give energy from outside, it will automatically proceed because it is going from high energy state to low energy state i.e., going to more stable state.