Gen Chem 1

Hf practice

Using standard enthalpies of formation, calculate ΔHorxn for the following:

1. C2H4(g) + H2(g) → C2H6(g)

2. 3NO2(g) + H2O(g) → 2HNO3(g) + NO(g)

3. Cr2O3(s) + 3CO(g) → 2Cr(s) + 3 CO2(g)

Hess’s Law practice

1. Calculate ΔHrxn for the following

   1. 3C(s) + 4H2(g) → C3H8(g)

Using the following information:

C3H8(g) + 5 O2(g) → 3CO2(g) + 4 H2O(g) ΔH = -2043 kJ

C(s) + O2(g) → CO2(g) ΔH = -393.5 kJ

2H2(g) + O2(g) → 2H2O(g) ΔH = -483.6 kJ

1. Calculate ΔHrxn for the following

   1. 3H2(g) + O3(g) → 3H2O(g)

Using the following information:

2 H2(g) + O2(g) → 2 H2O(g) ΔH = -483.6 kJ

3 O2(g) → 2 O3(g) ΔH = 285.4 kJ

Calorimetry & heat exchange

1. 12oz of water is heated from 22.0 oC to 98oC to make a cup of tea. How much heat is added to heat this water? The specific heat of water is 4.184 J/gC and the density of water is 1.00g/mL.

2. 1 Oreo contains 45 Calories. How many Joules are in 1 Oreo cookie? (Remember a Calorie is a nutritional Calorie. 1 Calorie = 1000 energy calories.)

3. If 0.158g Mg is combined with enough HCl to make 100.0mL of solution and the temperature rises from 25.6 oC to 32.8 oC, find ΔHrxn if the heat capacity of the solution is 4.184 J/gC and the density is 1.00g/mL.

   1. Hints: Calculate the qsoln. Remember that qsoln = -qrxn and that ΔHrxn = qrxn/ mol Mg

   2. The reaction is: Mg(s) + HCl(aq) → MgCl2(aq) + H2(g) … is the equation balanced?

Stoichiometry with Enthalpy

1. How much energy is released when 12.4g of Manganese reacts with hydrochloric acid if ΔHrxn=-221 kJ/mol?

2. How many grams of N2O2gas is required to decompose to absorb 15kJ of energy? ΔHrxn= 110 kJ/mol