Hess’s Law Conservation of Energy

Slides:

Advertisements

Similar presentations

Enthalpy of Neutralisation

Advertisements

Chemistry Tutorial 5: Q4 Sit Han Yu 12S7F. Question Sulfur dioxide is a major pollutant from sulfuric acid plants. The SO 2 emitted into the atmosphere.

Hess’s Law. Several reactions in chemistry occur in a series of steps, rather than just one step. For example, the following reaction explains the combustion.

Hess’s law calculations. 2C(s) + 3H 2 (g) + ½O 2 (g) → C 2 H 5 OH(l) C(s) + O 2 (g) → CO 2 (g) ∆H = –393 kJ mol –1 H 2 (g) + ½O 2 (g) → H 2 O(l) ∆H =

Calorimetry 6.03 Honors.

Hess’s Law EQ: Why is Hess’s Law a useful tool in solving for ∆Hrxn?

CHEMISTRY 161 Chapter 6

Lecture 4: Hess’s Law Reading: Zumdahl 9.5 Outline: Definition of Hess’ Law Using Hess’ Law (examples)

Using Standard Molar Enthalpies of Formation SCH4U0.

Copyright © Houghton Mifflin Company. All rights reserved. 10 | 1 Energy and Energy Changes Energy: ability to do work or produce heat –Chemical, mechanical,

Enthalpy of Neutralisation

Sections 5.4 – 5.6 Energy and Chemical Reactions.

Unit 3 PPA 1 Verification of Hess’s Law. Verification of Hess’s Law (Unit 3 PPA 1) The aim of the experiment is to show that the enthalpy change for a.

Standard Molar Enthalpies of Formation ΔHfoΔHfo. Focus Questions 1) What are formation reactions? 2) What is standard molar enthalpy of formation? 3)

Enthalpy Calculations

Energetics 6.1 What is Energetics?

Chemistry Chapter 7 – Hess’s Law Teacher: H. Michael Hayes.

Chapter 16 Calorimetry.

Lecture B. Day 4 Activities: Exothermic or endothermic? Objectives –Be able to identify exothermic and endothermic reactions based on temperature change.

Hess’s Law Review  Q - What is the first Law of Thermodynamics?

Title: Lesson 3 Hess’s Law and Enthalpy of Formation and Combustion Learning Objectives: – Define Hess’s Law – Using calculations show that enthalpies.

Chapter : Chemical Reactions That Involve Heat Suggested Reading: Pages

Bomb Calorimetry (Constant Volume Calorimetry)

Aim: What is entropy?.

Hess’s Law. Some enthalpy changes can not be measured directly in the lab. Hess’s Law is used to calculate these enthalpy changes Use the information.

Industrial Chemistry Hess’s law. Index Hess’s Law and its experimental verification Hess’s Law calculations, 4 examples. Hess’s Law.

Topic: Thermodynamics Do Now: packet p.1. Every physical or chemical change is accompanied by energy change  Energy released = _________________  Energy.

Hess’s Law of Additivity of Reaction Enthalpies 1.

Chapter 9 Lecture Basic Chemistry Fourth Edition 9.5 Energy in Chemical Reactions Learning Goal Given the heat of reaction (enthalpy change), calculate.

Mole, gas volume and reactions, Chemical energy and Enthalpy,

Bell Work. Take out a piece of paper

Chapter 10 Energy. 10 | 2 Energy and Energy Changes Energy: ability to do work or produce heat –Chemical, mechanical, thermal, electrical, radiant, sound,

Q-Hess’s Law Prem Sattsangi Copyright #2-Hess’s Law Study Please have your pencil and paper and BLB text book as you attempt these problem. Write.

SCH4U Thermodynamics. * Energy difference between the reactants and products. ΔH = H products - H reactants As long as pressure remains constant, the.

New Way Chemistry for Hong Kong A-Level Book 11 Chapter 6 Energetics 6.1 What is Energetics? 6.2 Ideal Enthalpy Changes Related to Breaking and Formation.

Topic: Enthalpy and Table I Do Now: packet p.1. Chemistry is the study of matter and energy. So far we have learned about the types of matter and how.

Standard Enthalpy of Formation Chapter 5.5 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Energy & Rates.

Industrial Applications of Chemical reactions

The basis for calculating enthalpies of reaction is known as Hess’s law: the overall enthalpy change in a reaction is equal to the sum of enthalpy changes.

ENERGY EXCHANGES IN CHEMICAL REACTIONS

Energy: Standard Enthalpy of Formation and Reaction – Direct & Hess’s Law Enthalpy Enthalpy (H): heat flow for a chemical reaction. q constant P.

3 Enthalpy. Units SI unit = joule 1KJ = 1000J = cal 1st law of Thermodynamics The total energy of the universe is constant i.e energy cannot be.

Exothermic and Endothermic Reactions. - What is Exothermic and Endothermic Reactions ? Exothermic reactions : Reactions accompanied with producing heat.

 Concerned with identifying the identity of a substance  Or whether a specific substance is present  i.e. flame test, litmus tests.

IIIIII Chapter 16 Hess’s Law. HESS’S LAW n If a series of reactions are added together, the enthalpy change for the net reaction will be the sum of the.

Thermodynamics. Every physical or chemical change is accompanied by energy change Thermodynamics = branch of chemistry that studies energy changes –Specifically:

Hess’s Law “In going from a particular set of reactants to a particular set of products, the change in enthalpy is the same whether the reaction takes.

 There is another way to calculate the heat of reaction, using bond enthalpies.  Bond enthalpy refers to the amount of energy stored in the chemical.

CHEMISTRY 122 Calculating the Heats of Reaction. Hess's Law  It is sometimes difficult to measure the change in enthalpy in a reaction because the reaction.

Section 2Chemical Reactions EQ: 〉 What is a chemical equation? 〉 What can a balanced chemical equation tell you?

© 2009, Prentice-Hall, Inc. Enthalpies of Formation An enthalpy of formation,  H f, is defined as the enthalpy change for the reaction in which a compound.

16.1(b) Hess’s Law 1 2 POINT > Recall enthalpies of reaction, formation and combustion POINT > Define Hess’s Law POINT > Use Hess’s law to determine.

How do we find the enthalpy of…

Hess’ Law energy changes are state functions. The amount of energy depends only on the states of the reactants and products, but not on the intermediate.

Industrial Chemistry Hess’s law.

Enthalpy = heat energy (H)

Can you handle the enthalpy?

Chemical Reaction Energy

In going from a particular set of reactants to a particular set of products, the change in enthalpy is the same whether the reaction takes place in one.

Heat and Enthalpy.

Hess’s Law & Standard Enthalpies of Formation

Unit 5: Thermochemistry

Chemical Energy 07/12/2018.

List of enthalpies for several kinds of reactions.

THERMOCHEMISTRY.

THERMOCHEMISTRY.

Enthalpy 18/04/2019.

Thermochemistry Lesson # 4: Hess’s Law.

LO: I understand what is meant by Hess’s law.

Presentation transcript:

Hess’s Law Conservation of Energy The overall enthalpy change in converting reactants to products is the same regardless of the route taken. Example A —>B (ROUTE 1) or A —>C —>B (ROUTE 2) A —>D —>E —>B ( ROUTE 3)

ΔH1 = route 1 ΔH2 + ΔH3 = route 2 ΔH4 + ΔH5 = route 3 Hess’s Law states the overall enthalpy change will be the same – therefore: ΔH1 = ΔH2 + ΔH3 or = ΔH4 + ΔH5

Uses of Hess’s Law We can use Hess’s Law to calculate enthalpy changes which are very difficult or impossible to do by experiment. Example The neutralisation of KOH using HCl. We can do this by adding KOH(s) directly to HCl(aq) – ΔH1 or Dissolving KOH(s) in water – ΔH2 then Adding KOH(aq) to HCl(aq) – ΔH3

Pathway 1. KOH(s) + HCl (aq) —> KCl (aq) + H2O(l) ΔH1 2. KOH(s) + H2O (aq) —> KOH (aq) ΔH2 3. KOH(aq) + HCl(aq) —>KCl (aq) + H2O ΔH3 According to Hess’s Law ΔH1 = ΔH2 + ΔH3

Examples Calculate the energy change for the reaction : RbCl(s) —> Rb+(g) + Cl-(g) Use the following enthalpy changes: RbCl(s) —> Rb+ (aq) + Cl- (aq) + 17 kJ Rb+ (g) —> Rb+ (aq) - 301 kJ Cl- (g) —> Cl- (aq) - 364 kJ

The Steps! 1. Write balanced eq for the reaction you wish to find the enthalpy change. 2. Write balanced eq for the reactions that have been given to you. 3. Label each step with an appropriate ΔH. Make sure you have identified more than one route for the reaction to follow. 4. Write down the enthalpy change for the direct route ( Hess’s Law) 5. Put in the values for each reaction.

1. RbCl (s) —> Rb+ (g) + Cl- (g) Δ H = ? 2. RbCl (s) —> Rb+ (aq) + Cl- (aq) Δ Ha Rb+ (g) —> Rb+(aq) Δ Hb Cl- (g) —> Cl- (aq) Δ H c 3. Route 1 = Δ H ? Route 2 = Δ H a + ( - Δ H b) + (- Δ H c) 4. Hess’s Law Δ H =Δ H a + ( - Δ H b) + (- Δ H c) 5. Δ H = +17 +(+301) + (+364) = + 682 kJ mol/l