Enthalpy Change in Chemical Reactions

Energy Changes

By Angela Toh

Multiple Choice

An increase or decrease in energy during a chemical reaction is called _____.

• Exothermic

• Endothermic

• Enthalpy

• Entropy

Multiple Choice

Exothermic reactions...

• Absorb energy
• Release energy
• Release Color
• Absorb Color

Multiple Choice

Exo means out or ________.

• absorbed

• released

Multiple Choice

In an endothermic reaction, heat is ...

• taken in or absorbed
• given out or released 

Multiple Choice

Endo means in or _______.

• absorbed

• released

Multiple Choice

Is this equation endo- or exo-thermic?

PCl₃ (s) + Cl₂ (g) --> PCl₅ (s) + energy

• endothermic

• exothermic

Multiple Choice

Is this equation endo- or exo-thermic?

2KNO₃ (s) + energy --> 2KNO₂ (s) + O₂

• endothermic

• exothermic

Multiple Choice

When the reaction occurs, the surrounding temperature goes up.

• endothermic

• exothermic

Multiple Choice

A reaction occurs in a test tube you are holding---it starts to feel cold to you.

• endothermic

• exothermic

Multiple Choice

Combustion reactions.

• endothermic

• exothermic

Multiple Choice

A reaction that uses energy.

• endothermic

• exothermic

Multiple Choice

You mix two solids and they get so cold they freeze a drop of water on the lab counter.

• endo

• exo

Multiple Choice

The reaction in hand warmer packs.

• endothermic

• exothermic

Multiple Choice

A student mixed two chemicals to allow them to react. The temperature before the reaction was 25 ° C. The temperature after the reaction was 18° C. Which of the following is true?

• It is an exothermic reaction

• It is an endothermic reaction

Multiple Choice

Is the combustion of gasoline endothermic or exothermic?

• Endothermic
• Exothermic

Multiple Choice

Which of the following process is exothermic?

• Candle wax melting

• A puddle evaporating

• Dry ice (solid carbon dioxide) subliming to form gaseous carbon dioxide

• Water freezing to form ice

Multiple Choice

Is this equation endo- or exo-thermic?

PCl₃ (s) + Cl₂ (g) --> PCl₅ (s) + energy

• endothermic

• exothermic

Multiple Choice

Is this equation endo- or exo-thermic?

2KNO₃ (s) + energy --> 2KNO₂ (s) + O₂

• endothermic

• exothermic

Multiple Choice

Is photosynthesis an exothermic or endothermic reaction?

• exothermic

• endothermic

Multiple Choice

Is respiration an exothermic or endothermic reaction?

• exothermic

• endothermic

Multiple Choice

Is condensation an exothermic or endothermic change?

• exothermic

• endothermic

Multiple Choice

Is neutralisation an exothermic or endothermic reaction?

• exothermic

• endothermic

Multiple Choice

Is decomposition an exothermic or endothermic reaction?

• exothermic

• endothermic

Multiple Choice

What statement describes an exothermic reaction?

• Products have more energy than reactants.

• Products have less energy than reactants.

• Products have the same energy as reactants.

• It is not possible to determine energy differences between products and reactants.

Multiple Choice

What statement describes an endothermic reaction?

• Products are higher in energy than reactants.

• Products are lower in energy than reactants.

• Products have the same energy as reactants.

• It is not possible to determine energy differences between products and reactants.

Multiple Choice

Symbol used for change in energy available as heat: 

• delta H
• delta S
• delta T
• delta G

Multiple Choice

delta H is: 

• enthalpy change
• entrophy change
• temperature change
• change in free energy

Multiple Choice

Endothermic reaction

• delta H > 0
• delta H < 0
• delta H = O

Multiple Choice

Endothermic reaction

• delta H is positive
• delta H is negative
• delta H is zero

Multiple Choice

Exothermic reactions:

• delta H < 0
• delta H > 0
• delta H + 0

Multiple Choice

Exothermic reaction:

• delta H is positive
• delta H is negative
• delta H is zero

Multiple Choice

Which letter corresponds to the energy of the products?

• A
• B
• C
• D

Multiple Choice

Which letter corresponds to the energy of the reactants?

• A
• B
• C
• D

Multiple Choice

Which letter corresponds to the activation energy of the forward reaction?

• A
• B
• C
• D

Multiple Choice

Based upon the graph above, what type of reaction is this?

• Endothermic

• Exothermic

Multiple Choice

In the graph above, what does D represent?

• activation energy

• products

• reactants

• enthalpy change

Multiple Choice

Which letter in the image above represents the products.

• A

• B

• C

• D

Multiple Choice

The following equation shows the formation of magnesium oxide from magnesium metal. Which statement is correct for this reaction?

2Mg(s) + O₂(g) → 2MgO(s) ΔH = -1204 kJ

• 1204 kJ of energy are released for every mole of magnesium reacted

• 602 kJ of energy are absorbed for every mole of magnesium oxide formed

• 602 kJ of energy are released for every mole of oxygen reacted

• 1204 kJ of energy are released for every two moles of magnesium oxide formed

Multiple Choice

Does breaking bonds require energy, release energy, or not involve energy at all?

• requires energy to break

• releases energy when broken

• No energy involved

Multiple Choice

Which statements about exothermic reactions are correct?

I. They have negative ΔH values II. The products have a lower enthalpy than the reactants III. The products are more energetically stable than the reactants

• I and II only

• I and III only

• II and III only

• I, II, and III

Multiple Choice

The average bond enthalpies for O-O and O=O are 146 and 496 kJ/mol respectively. What is the enthalpy change, in kJ, for the reaction below?

H₂O₂(g) → H₂O(g) + ½O₂(g)

• -102

• +102

• +350

• +394

Multiple Choice

Calculate the enthalpy change, in kJ, for this dissociation of mole of propan-1-ol.

C₃H₇OH(g) ⟶ 3C(g) + 8H(g) + O(g)

• −4751

• −4403

• +4403

• +4751

Multiple Choice

Hydrogen is produced by the reaction of methane with steam. The reaction mixture reaches a state of dynamic equilibrium.

CH₄(g) + H₂O(g) ⇌ CO(g) + 3H₂(g) ∆H = +206 kJ mol⁻¹

Some enthalpy data is given in the table.

Use the information in the table and the stated enthalpy change to calculate the missing bond enthalpy.

• 234

• 1064

• 1476

• 1936

Multiple Choice

Given the data in the image which one of the following is the enthalpy change, in kJ mol⁻¹, of the reaction below?

CH₄(g) → C(s) + 4H(g)

• −947

• +511

• +797

• +947