For which of the following does the enthalpy of reaction (ΔHrxn) correspond to the standard molar enthalpy of formation (ΔH°f) for the product? Fe(l) + Cl2(g) → FeCl2(s) 2N(g) + 4O(g) → N2O4(g) N2(g) + 2O2(g) → N2O4(g) C2H4(g) + H2(g) → C2H6(g)

A 0.470-g sample of magnesium reacts with 200 g dilute HCl in a coffee-cup calorimeter to form MgCl2(aq) and H2(g). The temperature increases by 10.9 C as the magnesium reacts. Assume that the mixture has the same specific heat as water and a mass of 200 g. (a) Calculate the enthalpy change for the reaction. Is the process exothermic or endothermic? (b) Write the chemical equation and evaluate H.

The enthalpy change for the following reaction is 393.5 kJ. C(s,graphite)+O2(g)CO2(g) (a) Is energy released from or absorbed by the system in this reaction? (b) What quantities of reactants and products are assumed? (c) Predict the enthalpy change observed when 3.00 g carbon burns in an excess of oxygen.

Another reaction that is used to propel rockets is N2O4(l)+2N2H4(l)3N2(g)+4H2O(g) This reaction has the advantage that neither product is toxic, so no dangerous pollution is released. When the reaction consumes 10.0 g liquid N2O4, it releases 124 kJ of heat. (a) Is the sign of the enthalpy change positive or negative? (b) What is the value of H for the chemical equation if it is understood to be written in molar quantities?