Endothermic & Exothermic Reactions Practice Problems

Identify the correct statement about the heat of a reaction.

Is the following endothermic or exothermic?

Solid iodine sublimes to a purple vapor which is iodine gas.

Identify whether the following is endothermic or exothermic:

Digested food provides energy to every cell in the body.

Consider the reaction:

C₂H₆(g) + O₂(g) → CO₂(g) + H₂O(g) + 1561 kJ

Determine whether the reaction is endothermic or exothermic.

The reaction between silicon and fluorine produces silicon tetrafluoride, as shown below.

Si(s) + 2 F₂(g) → SiF₄(g) + 1615 kJ

Determine whether the energy of the product is lower or higher than that of the reactants.

Determine whether the following is endothermic or exothermic:

The reactants have lower energy levels than the products.

If ΔH = —129.78 kcal/mol(—543 kJ/mol) and K = 1.22 at 25 °C for the formation of phosphoryl chloride from the reaction of phosphorus trichloride and oxygen gas, 

2 PCl₃(g) + O₂(g) → 2 POCl₃(g)

Is the reaction exothermic or endothermic?

At 25.0 °C, the ΔH and K for the conversion of dinitrogen tetroxide to nitrogen dioxide are +13.68 kcal/mol (+57.24 kJ/mol) and 0.9989, respectively.

 N₂O₄(g) ⇌ 2 NO₂(g)

Is the reaction endothermic or exothermic?

The energy required for the vaporization of hydrogen cyanide (HCN) from liquid to gas is 6.26 kcal/mol (26.2 kJ/mol). Determine the sign for ΔH and write a reaction showing heat as either a reactant or product.

True or False. In an endothermic process, the total enthalpy of the reactants is greater than the total enthalpy of the products.

During an alcoholic fermentation, yeast converts glucose (C₆H₁₂O₆) into ethanol (CH₃CH₂OH) and carbon dioxide.

C₆H₁₂O₆(aq) → 2 CH₃CH₂OH(aq) + 2 CO₂(g)

Is the process exothermic or endothermic?

Identify the exothermic reaction(s).

a) AgCl (s) → Ag⁺ (aq) + Cl^– (aq); ΔH = 127 kJ/mol

b) 2 Mg (s) + O₂ (g) → 2 MgO (s); ΔH = –1203 kJ/mol

c) Na₂SO₄ • 10 H₂O (s) → Na₂SO₄ (aq) + 10 H₂O (l); ΔH = 74 kJ/mol

d) 2 Al (s)+ Fe₂O₃(s) ⟶ 2 Fe (s) + Al₂O₃ (s); ΔH = −852 kJ/mol

e) 2 Fe₂O₃ (s) + 3 C (s) → 4 Fe (s) + 3 CO₂ (g); ΔH = 468 kJ/mol

f) CaO (s) + H₂O (l) → Ca(OH)₂ (s); ΔH = −65.2 kJ/mol

When the system releases heat to the surroundings, the sign of Δq is ______ and the process is ______.

Which among the processes below is expected to be endothermic?

In the following illustration, the contents of each closed box represent a system, while the arrows show the changes to the system during some process. The relative magnitudes of q and w are represented by the lengths of the arrows. Which of the processes is endothermic?

When mothballs (naphthalene), C₁₀H₈(s), sublime to the gas phase to form C₁₀H₈(g), how does heat interact with the surroundings, and is the process endothermic or exothermic?