Hess's Law and the Enthalpy of Combustion of Magnesium Magnesium ribbon burns in air in a highly exothermic combustion reaction. (See equation (1) below.) A very bright flame accompanies the production of magnesium oxide. It is impractical and dangerous to use a simple calorimeter to determine the enthalpy change for this reaction: (1) Mg(s) + O₂(g) → MgO(s) Instead, you will determine the enthalpy changes for two other reactions (equations (2) and (3) below). You will use these enthalpy changes, along with the known enthalpy change for another reaction (equation (4) below), to determine the enthalpy change for the combustion of magnesium. (2) MgO(s) + 2HCl(aq) → MgCh(aq) + H₂O(l) (3) Mg(s) + 2HCl(aq) → MgCl₂(aq) + H₂(g) (4) H₂(g) + — O₂(g) → H₂O(Z) + 285.8 kJ Notice that reactions represented in equations (2) and (3) occur in aqueous solution. You can use a simple calorimeter to determine the enthalpy changes for these reactions. Equation (4) represents the formation of water directly from its elements in their standard state. Pre-Lab Questions 1. Explain how Hess's law allows you to determine the enthalpy of a reaction without carrying out the reaction. 2. What type of data do you need in order to use Hess's law?
Hess's Law and the Enthalpy of Combustion of Magnesium Magnesium ribbon burns in air in a highly exothermic combustion reaction. (See equation (1) below.) A very bright flame accompanies the production of magnesium oxide. It is impractical and dangerous to use a simple calorimeter to determine the enthalpy change for this reaction: (1) Mg(s) + O₂(g) → MgO(s) Instead, you will determine the enthalpy changes for two other reactions (equations (2) and (3) below). You will use these enthalpy changes, along with the known enthalpy change for another reaction (equation (4) below), to determine the enthalpy change for the combustion of magnesium. (2) MgO(s) + 2HCl(aq) → MgCh(aq) + H₂O(l) (3) Mg(s) + 2HCl(aq) → MgCl₂(aq) + H₂(g) (4) H₂(g) + — O₂(g) → H₂O(Z) + 285.8 kJ Notice that reactions represented in equations (2) and (3) occur in aqueous solution. You can use a simple calorimeter to determine the enthalpy changes for these reactions. Equation (4) represents the formation of water directly from its elements in their standard state. Pre-Lab Questions 1. Explain how Hess's law allows you to determine the enthalpy of a reaction without carrying out the reaction. 2. What type of data do you need in order to use Hess's law?
Chemistry
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Author:Steven S. Zumdahl, Susan A. Zumdahl, Donald J. DeCoste
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Chapter1: Chemical Foundations
Section: Chapter Questions
Problem 1RQ: Define and explain the differences between the following terms. a. law and theory b. theory and...
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Thermochemistry
Thermochemistry can be considered as a branch of thermodynamics that deals with the connections between warmth, work, and various types of energy, formed because of different synthetic and actual cycles. Thermochemistry describes the energy changes that occur as a result of reactions or chemical changes in a substance.
Exergonic Reaction
The term exergonic is derived from the Greek word in which ‘ergon’ means work and exergonic means ‘work outside’. Exergonic reactions releases work energy. Exergonic reactions are different from exothermic reactions, the one that releases only heat energy during the course of the reaction. So, exothermic reaction is one type of exergonic reaction. Exergonic reaction releases work energy in different forms like heat, light or sound. For example, a glow stick releases light making that an exergonic reaction and not an exothermic reaction since no heat is released. Even endothermic reactions at very high temperature are exergonic.
Question
Please help me answer the pre lab questions and what is the molar enthalpy of combustion of magnes
Transcribed Image Text:Skill Check
SHANKKEEN
Performi and Recording
✓Analyzing and haterpreting
Safety Precautions
• Hydrochloric acid is corrosive.
Use care when handling it.
Hydrochloric acid fumes also cause
burning to the linings of the nose
and throat when inhaled.
. Be careful not to inhale the
magnesium oxide powder.
Materials
- 1.00 mol/L HCl(aq)
- MgO(s) powder
- Mg ribbon (or Mg turnings)
• simple calorimeter
. 100 mL graduated cylinder
Scoop
- electronic balance
.thermometer (alcohol or digital)
. sandpaper or emery paper
5-B
Hess's Law and the Enthalpy of Combustion
of Magnesium
Magnesium ribbon burns in air in a highly exothermic combustion reaction.
(See equation (1) below.) A very bright flame accompanies the production of
magnesium oxide. It is impractical and dangerous to use a simple calorimeter to
determine the enthalpy change for this reaction:
(1) Mg(s) + + O₂(g) → MgO(s)
Instead, you will determine the enthalpy changes for two other reactions
(equations (2) and (3) below). You will use these enthalpy changes, along
with the known enthalpy change for another reaction (equation (4) below), to
determine the enthalpy change for the combustion of magnesium.
(2) MgO(s) + 2HCl(aq) → MgCh(aq) + H₂O(2)
(3) Mg(s) + 2HCl(aq) → MgCl₂(aq) + H₂(g)
(4) H₂(g) + + O₂(g) → H₂O(Z) + 285.8 kJ
Notice that reactions represented in equations (2) and (3) occur in aqueous
solution. You can use a simple calorimeter to determine the enthalpy changes for
these reactions. Equation (4) represents the formation of water directly from its
elements in their standard state.
Pre-Lab Questions
1. Explain how Hess's law allows you to determine the enthalpy of a reaction
without carrying out the reaction.
2. What type of data do you need in order to use Hess's law?
3. Describe the safety precautions you must follow when working with a
strong acid.
Question
What is the molar enthalpy of combustion of magnesium?
338 MHR.Unit 3 Energy Changes and Rates of Reaction
When magnesium ribbon burns
In air a very bright white flame
is produced. The lower part of
the ribbon shown here has been
converted to the solid, white
magnesium oxide product.
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