Enthalpy Change

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

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

• −1.9

• +1.9

• −788.9

• +788.9

Consider the following bond enthalpy values.

O−O = +146 kJ/mol

O−H = +463 kJ/mol

O=O = +496 kJ/mol

For the reaction

H−O−O−H _(g) → H−O−H _(g) + ½O=O _(g)

the enthalpy change, in kJ/mol, is ...

• −102

• +102

• +350

• +394

Using the data in the table below, calculate the standard enthalpy change, in kJ/mol, for the reaction between carbon disulfide, CS₂, and oxygen shown in the following equation.

CS_{2 (g)} + 3O_{2 (g)} → CO_{2 (g)} + 2SO_{2 (g)}

• −570

• −790

• −860

• −1080

Consider the following information of bond energy:

H−H = +436 kJ/mol

I−I = +151 kJ/mol

H−I = +299 kJ/mol

For the reaction:

H_{2 (g)} + I_{2 (g)} → 2HI _(g)

the enthalpy change, in kJ/mol is...

• +288

• +144

• −11

• −5.5

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

The enthalpy change for the reaction between hydrochloric acid and sodium hydroxide is −56 kJ/mol. Therefore ...

• the reaction is exothermic and the temperature rises

• the reaction is exothermic and the temperature falls

• the reaction is endothermic and the temperature rises

• the reaction is endothermic and the temperature falls

Which of these diagram correctly represent an endothermic reaction?

• 
• 
• 
• 

Some mean bond enthalpy values are given in the table below.

H−H = +436 kJ/mol

I−I = +151 kJ/mol

H−I = +299 kJ/mol

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

H_{2 (g)} + I_{2 (g)} → 2HI _(g)

• 436 + 151 − 299 = + 288

• −436 − 151 + 299 = − 288

• +436 + 151 − (2 x 299) = − 11

• −436 − 151 + (2 x 299) = +11

In an endothermic reaction in aqueous solution, which of the following is correct?

• temperature increases, sign of enthalpy change is positive

• temperature increases, sign of enthalpy change is negative

• temperature decreases, sign of enthalpy change is positive

• temperature decreases, sign of enthalpy change is negative

Example of endothermic reaction is ...

• Combustion

• Photosynthesis

• Neutralization

• Respiration