Endothermic & Exothermic Reactions Practice Problems

An ice cube was accidentally left on a table. Over time, the ice cube melts. Determine the sign of the change in enthalpy for the melting of ice.

Consider the process shown below. Determine the sign of ΔH and classify the process as endothermic or exothermic.

Which process below has the correct sign for ΔHº and incorrect classification (endothermic or exothermic)?

If the following reactions are separately reacted in a chamber, which one will increase the temperature of the chamber?

(i) 6 CO₂ (g) + 6 H₂O (l) → C₆H₁₂O₆ (s) + 6 O₂ (g)

(ii) HCO₃^- (aq) + H⁺ (aq) → H₂O (aq) + CO₂(aq)

(iii) H₂O (l) + HCl (aq) → H₃O⁺ (aq) + Cl^- (aq)

(iv) C₆H₁₂O₆ (s) + 6 O₂ (g) → 6 CO₂ (g) + 6 H₂O (l)

Is the following process endothermic or exothermic?
The dissociation of N₂O₄ molecules into nitrogen gas and oxygen gas with the following equation

N₂O₄ (g) → N₂ (g) + 2 O₂ (g)

Is the following process endothermic or exothermic?

The solidification of water to the ice at standard conditions.

Without considering specific values, identify the sign of enthalpy change of reaction for CaS(s) → Ca²⁺(g) + S^2-(g)

Consider a block of ice placed in a tub of water at room temperature. If the ice is considered the thermodynamic system, what happens to the temperature of the system? Identify if the process is exothermic or endothermic.

Consider the decomposition of hydrogen peroxide to water and oxygen: 

2 H₂O₂(l) → 2 H₂O(l) + O₂(g)       ΔH = -196 kJ

If hydrogen peroxide was in solid phase, would the enthalpy of reaction change? If so, will it decrease or increase?

Without looking up specific values, identify which between 5 g of O₂(g) and 5 g of O₂(l) has greater enthalpy at the same temperature.

Carbon can react with oxygen and produce CO₂ and CO:

C(s) + O₂(g) → CO₂(g) ΔH = -393.5 kJ

C(s) + 1/2 O₂(g) → CO(g) ΔH = -110.5 kJ

However, CO₂ production is much more favorable than CO being produced. Why is this the case? 

The reaction below shows an electron transfer: 

X(g) + X(g) → X⁺(g) +  X^-(g)

Is this process expected to be exothermic for bromine? 

The boxes below represent a thermodynamic system. The arrows pertain to the direction of heat and work applied or taken from the system with the length corresponding to their relative magnitudes. Identify which of the processes is endothermic. 

Potassium reacts intensely with water, forming potassium hydroxide and highly flammable hydrogen. The reaction can even cause a small explosion due to the heat released igniting the hydrogen. If the reverse reaction was done where potassium hydroxide and hydrogen were reacted, will the heat be a product or a reactant?

A tire filled with air was placed in an ice bath. The tire shrank by a small amount due to cooling and the water pressure. Calculate the change in internal energy if 5.6 kJ of heat was removed and 2.5 kJ was work done by water. Identify if the process is exothermic or endothermic. 

Identify the sign of enthalpy change for each process below. 

a. Formation of morning dew on plants

b. Burning wood

c. Formation of dry ice fog

Identify each as either endothermic or exothermic 

a. Formation of morning dew on plants

b. Burning wood

c. Formation of dry ice fog

For an endothermic reaction with w = 0, determine the signs of ΔH and ΔE.

Consider the given figure, where a container is placed in a tub of water.

If the system is defined as the contents of the container and heat is able to flow through the container walls, identify the changes that will occur in the temperature of the system and surroundings. Identify the sign of q associated with each change. Is the process exothermic or endothermic in reference to the system.

Consider the following reaction:
H₂(g) → H(g) + H(g)

Would you expect the magnitude of ΔH to increase, decrease, or stay the same if H₂(l) were consumed instead of H₂(g)?

Is the forward or reverse reaction more thermodynamically favored?

CO(g) + 1/2 O₂(g) → CO₂(g); ΔH° = –283.0 kJ/mol

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

Determine the signs for an endothermic reaction given w = 0:

a. +ΔH and -ΔE

b. -ΔH and +ΔE

c. -ΔH and -ΔE

d. +ΔH and +ΔE

Which of the following statements are true?

a. For an exothermic reaction, ΔH > 0.

b. For an endothermic reaction, ΔH > 0.

c. An example of an exothermic process is the melting of ice.

d. An example of an exothermic process is combustion.

e. ΔH < 0 when energy is transferred (as q) from the system to the surroundings.

f. ΔH < 0 when energy is transferred (as q) from the surroundings to the system.

Predict whether the following reactions will be exothermic or endothermic.

a. N₂(g) + 3 H₂(g) → 2 NH₃(g)

b. S(g) + O₂(g) → SO₂(g)

c. CaO₃(s) → CaO(s) + CO₂(g)

d. 2 H₂O(g) → 2 H₂(g) + O₂(g)

e. 2 F(g) → F₂(g)

What effect does an exothermic reaction have on its surroundings?

Why do the surroundings feel colder during an endothermic reaction?

Which of the following is required to break a bond between atoms?

Without referring to thermodynamic values, does 2 mol of O atoms have a higher enthalpy than 1 mol of O₂?

Glucose (C₆H₁₂O₆) can undergo decomposition to produce acetic acid (C₂H₄O₂). 

 C₆H₁₂O₆(s) → 2 C₂H₄O₂(l) ΔH = 304.7 kJ/mol

Is the reverse reaction more thermodynamically favored to occur than the forward reaction?

Sulfur dioxide gas can be produced by heating up solid sodium sulfite. 

Na₂SO₃(s) → Na₂O(s) + SO₂(g) ΔH = −697 kJ/mol 

When heated, Na₂SO₃ decomposes spontaneously. Is the reverse reaction, the formation of Na₂SO₃ from Na₂O and SO₂, spontaneous under normal conditions? Please explain.

2.50 g of solid silver nitrate was dissolved in 150 g of water in a coffee-cup calorimeter. 

AgNO₃(s) → Ag⁺(aq) + NO₃⁻(aq)

Is the process exothermic or endothermic if the temperature drops from 29.3 to 28.2 °C?