Question

Consider the following reaction. CH3OH(g) CO(g) + 2 H2(g)

DELTA-H = +90.7 kJ

(a) Is the reaction exothermic or endothermic?

(b) Calculate the amount of heat transferred when 45.0 g of CH3OH(g) are decomposed by this reaction at constant pressure.

DELTA-H =___ kJ

(c) If the enthalpy change is 20.0 kJ, how many grams of hydrogen gas are produced?

_____g

(d) How many kilojoules of heat are released when 11.5 g of CO(g) reacts completely with H2(g) to form CH3OH(g) at constant pressure?

DELTA-H = ___kJ

(e) Calculate DELTA- E when 670.0 g of CH3OH(g) completely reacts at a constant temperature of 300 K and constant pressure of 0.95 atm.

R = 8.314 J/mol*K

and R = 0.08206 atm*L/mol*K

Answer 1

  (a) Since the deltaH is positive, it means that the products have more energy than the reactants. This means that the reaction is endothermic.

(b) 45.0 g CH₃OH x (1 mol CH₃OH / 32 g CH₃OH) x (90.7 kJ / 1 mol CH₃OH) = 127.55 kJ

(c) 20.0 kJ x (2 mol H₂ / 90.7 kJ) x (2 g H₂ / 1 mol H₂) = 0.882 g H₂

(d) 11.5 g CO x (1 mol CO / 28 g CO) x (-90.7 kJ / 1 mol CO) = -37.25 kJ
Since the value of delta H is the negative for the reverse reaction, we used -90.7 kJ here. The final answer is negative because the reaction gives off heat energy to the surrounding environment.