Hess's Law

Consider the following reactions:Fe(s) + 1/2 O2(g) --> FeO(s) H= -272.0 kJ2 Fe(s) + 3/2 O2(g) --> Fe2O3(s) H= -825.5 kJDetermine the delta H for the reaction: 2 FeO(s) + 1/2 O2(g) --> Fe2O3

• -281.5 kJ

• -1097.5 kJ

• -1369.5 kJ

• 281.5 kJ

Tags

NGSS.HS-PS1-4

NGSS.HS-PS3-1

The enthalpy change for the reaction, ∆H_r , is equal to 

• ∆H₁ + ∆H₂

• ∆H₁ - ∆H₂

• -∆H₁ - ∆H₂

• -∆H₁ + ∆H₂

Tags

NGSS.HS-PS1-4

Using the equations below:

C_(s) + O_2(g) → CO_2(g) ∆H = –390 kJ
Mn_(s) + O_2(g) → MnO_2(s) ∆H = –520 kJ

what is ∆H (in kJ) for the following reaction?

MnO_2(s) + C_(s) → Mn_(s) + CO_2(g)

• 910

• 130

• -130

• -910

Tags

NGSS.HS-PS3-1

For Hess' Law to be used what must be the same for all of the reactions being studied?

• The initial conditions of pressure and temperature.

• The final conditions of pressure and temperature.

• The initial and the final conditions of pressure and temperature.

• The initial and the final conditions of pressure and temperature, and the number of moles of reactants.

The thermochemical equation for the incomplete combustion of carbon into carbon monoxide is represented as: 2C (s) + O₂(g) --> 2CO(g) Compute for the H of the reaction if the overall process above can occur in two steps whose thermochemical equations are given below: (1) C _(s) + O_2(g) --> CO_2(g) H= -392.5 kJ (2) 2 CO_(g) + O_2(g) --> 2CO_2(g) H= -566.0 kJ

• 172.5 kJ

• 1,353 kJ

• -221.0 kJ

• 959.5 kJ

Tags

NGSS.HS-PS3-1

• -110.5 kJ

• 110.5 kJ

• -676.5 kJ

• 676.5 kJ

Tags

NGSS.HS-PS1-4

• -724.7 kJ

• 724.7 kJ

• -1085.7 kJ

• 1085.7 kJ

Tags

NGSS.HS-PS1-4

NGSS.HS-PS3-1

Which of the following statements best describes Hess's Law?

• The enthalpy change of a reaction is dependent on the pathway taken.

• The enthalpy change of a reaction is independent of the pathway taken.

• The enthalpy change of a reaction is always positive.

• The enthalpy change of a reaction is always negative.

• 483.6 kJ

• -483.6 kJ

• 241.8 kJ

• -241.8 kJ

Tags

NGSS.HS-PS3-1

• 890.3 kJ/mol

• -890.3 kJ/mol

• 445.15 kJ/mol

• -445.15 kJ/mol

Tags

NGSS.HS-PS3-1