Enthalpy Calculations

ΔH value in an endothermic reaction is a positive number.

• True
• False

What type of reaction is shown in the reaction pathway?

• endothermic reaction
• exothermic reaction

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NGSS.HS-PS1-4

How do you calculate Enthalpy of a reaction?

• ΔH = ΔH_products - ΔH_reactants

• ΔT = q / mC

• ΔG = ΔH -TΔS

• E = mc²

Calculate the enthalpy of the following reaction:
Ca(OH)₂ -> CaO + H₂O
ΔHf in kJ/mol:  
      Ca(OH)₂  -983.2
        CaO         -634.9
        H₂O         -285.5

• 62.8 kJ
• -62.8 kJ
• -1840.6
• 1840.6

Tags

NGSS.HS-PS1-4

NGSS.HS-PS3-1

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-PS1-4

NGSS.HS-PS3-1

Consider the following equations.

Mg_(s) + O_2(g) → MgO_(s) ∆H = –602 kJ

H_2(g) + O_2(g) → H₂O_(g) ∆H = –242 kJ

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

MgO_(s) + H_2(g) → Mg_(s) + H₂O_(g)

• -844

• -360

• +360

• +844

Tags

NGSS.HS-PS1-4

The standard enthalpy changes of formation of carbon dioxide and of methanoic acid are −394 kJ/mol and −409 kJ/mol respectively. Calculate the enthalpy change for the reaction

H_{2 (g)} + CO_{2 (g)} → HCOOH _(l)

• −803 kJ/mol

• −15 kJ/mol

• +803 kJ/mol

• +15 kJ/mol

Tags

NGSS.HS-PS1-4

NGSS.HS-PS3-1

The standard enthalpy change for the combustion of graphite is −393.5 kJ/mol and that of diamond is −395.4 kJ/mol.

What is the enthalpy change for the reaction below, in kJ/mol?

C _{(s, graphite)} → C _{(s, diamond)}

• −1.9

• +1.9

• −788.9

• +788.9

Tags

NGSS.HS-PS1-4

• endothermic reaction

• exothermic reaction

• reaction with catalyst

• equilibrium reaction

Tags

NGSS.HS-PS1-4

NGSS.HS-PS3-1

Use the H_f values in the table below to answer questions a and b about the following reaction.

CO_2(g) + N_2(g) ⟶ NO_(g) + CO_(g) ΔH = ?

Formula kJ/mol

CO(g) -110

CO2(g) -394

NO(g) 90

a) Calculate Hrxn for the reaction.

• 370kJ/mol

• 374kJ/mol

• 333kJ/mol

• 335KJ/mol

Tags

NGSS.HS-PS1-4