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08786cd6-efb7-4e90-aa4e-e2f751206045 Exothermic Summary A reaction that releases heat to the surroundings.

731c63f0-388c-4ddc-a8bc-30a23a39d0b8 Application on Hess’s Law medium Summary Question 1: Given the following reactions and their respective enthalpy changes: C(s) + O2(g) → CO2(g) ΔH1 = -393.5 kJ/mol H2(g) + 1/2O2(g) → H2O(l) ΔH2 = -286.0 kJ/mol C(s) + H2(g) → CH4(g) ΔH3 = -74.8 kJ/mol Calculate the enthalpy change for the reaction: CH4(g) + 2O2(g) → CO2(g) + 2H2O(l) Answer 1: To calculate the enthalpy change for the given reaction, we can use Hess's Law. By manipulating the given reactions, we can cancel out the common compounds and add the enthalpy changes. Multiplying reaction 1 by 2 gives: 2C(s) + 2O2(g) → 2CO2(g) 2ΔH1 = 2(-393.5 kJ/mol) = -787.0 kJ/mol Multiplying reaction 2 by 2 gives: 2H2(g) + O2(g) → 2H2O(l) 2ΔH2 = 2(-286.0 kJ/mol) = -572.0 kJ/mol Adding reactions 3, 2, and 1 gives: C(s) + H2(g) + 2H2(g) + O2(g) + 2O2(g) → CH4(g) + 2H2O(l) + 2CO2(g) ΔH3 + 2ΔH2 + 2ΔH1 = -74.8 kJ/mol + (-572.0 kJ/mol) + (-787.0 kJ/mol) = -1433.8 kJ/mol Since the given reaction is the reverse of the calculated reaction, the enthalpy change for the given reaction is the negative of the calculated value. ΔH = -(-1433.8 kJ/mol) = 1433.8 kJ/mol Question 2: Given the following reactions and their respective enthalpy changes: 2SO2(g) + O2(g) → 2SO3(g) ΔH1 = -198.2 kJ/mol S(s) + O2(g) → SO2(g) ΔH2 = -296.8 kJ/mol 2S(s) + 3O2(g) → 2SO3(g) ΔH3 = -792.0 kJ/mol Calculate the enthalpy change for the reaction: 2SO2(g) + O2(g) → 2SO3(g) + 198.2 kJ Answer 2: To calculate the enthalpy change for the given reaction, we can use Hess's Law. By manipulating the given reactions, we can cancel out the common compounds and add the enthalpy changes. Multiplying reaction 2 by 2 gives: 2S(s) + 2O2(g) → 2SO2(g) 2ΔH2 = 2(-296.8 kJ/mol) = -593.6 kJ/mol Adding reactions 1 and 2 gives: 2SO2(g) + O2(g) + 2S(s) + 2O2(g) → 2SO3(g) + 2

0081d36b-82f6-4a1c-bb1c-6494a4f26655 Atoms Summary The smallest unit of an element that retains the chemical properties of that element.

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< Back Hydrogen gas Part 1 Physical properties of hydrogen 1. Colorless odorless gas 2. Neutral to litmus 3. Less dense than air (so collected by upward delivery) 4. Insoluble in water (can be collected over water) 5. Highly flammable Reaction of Hydrogen Gas with Air Reacts with air violently (oxygen) when in contact with a flame. So it makes a squeaky pop with a lit splint 2H2(g) + O2 --> 2H2O Isotopes of Hydrogen Isotopes are atoms of the same element which have the same number of protons (atomic number) but different number of neutrons (mass number). Preparation of Hydrogen gas First : in Laboratory 1-Preparing hydrogen from water or steam Addition of Very reactive metals (example potassium , Sodium , Lithium , Calcium) + liquid water gives hydrogen gas and metal hydroxide. or Addition of metals to steam to produce metal oxide and hydrogen gas 2- Preparing Hydrogen from acids Addition of moderately reactive metals like magnesium aluminum zinc or iron to dilute hydrochloric acid or sulfuric acid Note that less reactive metals can not be used to prepare the hydrogen with dilute acids generally metals which are less reactive than hydrogen can not be used Second : Industrially 1-Using hydrocarbons example by heating a hydrocarbon like methane with steam using a catalyst like nickel , the product is Carbon monoxide and hydrogen gas The carbon monoxide produced can be reheated with more steam using an iron oxide catalyst to produce Carbon dioxide and hydrogen gas 2-Using coke Coke is a fuel made of coal The coke is reacted with steam at high temperature (around 1000) degrees celsius to produce carbon monoxide gas and hydrogen gas 3-Using Electrolysis Electrolysis is the breakdown of a substance using electric current the water is broken down by electrolysis into hydrogen and oxygen Or the NaCl solution (brine) is broken down into chlorine and Hydrogen gases Previous Next

AP Chemistry Study Guides Have Many Doubts , Study First! Unit 1 AP Chemistry Topic 1 The Mole Concept This is Unit 1 AP Chemistry The Mole Concept Read More Unit 1 AP Chemistry Topic 1 Masses and Particles This is Unit 1 AP Chemistry The Mole Concept Read More Unit 1 AP Chemistry Topic 1 Molar Mass This is Unit 1 AP Chemistry The Mole Concept Read More Unit 1 AP Chemistry Topic 2 Mass Spectra of Elements Read More Unit 1 AP Chemistry Topic 3 Elements and Mixtures Read More Unit 1 AP Chemistry Topic 4 Atoms and Electrons Read More Unit 1 AP Chemistry Topic 5 Periodic Trends Read More Unit 2 AP Chemistry Topic 1.1 Study Guide Chemical Bonding Read More Unit 7 AP Chemistry Questions Part 2 FRQ Continue Unit 7 Questions Read More Unit 7 AP Chemistry Questions Part 3 MCQ Continue Unit 7 Questions Read More Unit 7 AP Chemistry Questions FRQ Explore key concepts of chemical equilibrium, including dynamic balance, equilibrium constants (K), Le Chatelier's Principle, and real-world applications of reversible reactions. Read More Unit 7 AP Chemistry Equilibrium Part 1 Read More Unit 8 AP Chemistry Topic 1 Self Check Guide Unit 8 Self Study and Check Guide Read More Unit 8 AP Chemistry Topic 2 Self Check Guide Copy Unit 8 Self Study and Check Guide Read More Unit 8 AP Chemistry Topic 3 Self Check Guide Copy Copy Unit 8 Self Study and Check Guide Read More Unit 8 AP Chemistry Topic 4 Self Check Guide Copy Copy Copy Copy Copy Unit 8 Self Study and Check Guide Read More Unit 8 AP Chemistry Topic 4 Self Check Guide Copy Copy Copy Unit 8 Self Study and Check Guide Read More Unit 8 AP Chemistry Topic 4 Self Check Guide Copy Copy Unit 8 Self Study and Check Guide Read More Unit 8 AP Chemistry Topic 4 Self Check Guide Copy Unit 8 Self Study and Check Guide Read More Unit 8 AP Chemistry Topic 7 Self Check Guide Buffers Unit 8 Self Study and Check Guide Read More Unit 9 AP Chemistry Study Guide 1 Unit 9 Part 1 Read More Unit 9 AP Chemistry Study Guide 2 Unit 9 Part 2 Read More

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AP Chemistry Study Guides Unit 1 Revision Guide Atomic structure includes the study of subatomic particles, electron configurations, and periodic trends. Read More Unit 2 Revision Guide Chemical reactions involve the rearrangement of atoms to form new substances. This unit covers balancing chemical equations, types of reactions, and stoichiometry. Read More Unit 3 Revision Guide Thermochemistry deals with the energy changes in chemical reactions. Topics include heat transfer, calorimetry, enthalpy, and Hess's Law. Read More Unit 4 Revision Guide Chemical equilibrium is a dynamic balance between forward and reverse reactions. This unit covers equilibrium constants, Le Chatelier's principle, and factors affecting equilibrium. Read More Unit 5 Revision Guide Electrochemistry studies the relationship between chemical reactions and electricity. Topics include redox reactions, electrochemical cells, Faraday's laws, and electrolysis. Read More Unit 6 Revision Guide Read More Unit 7 Revision Guide Read More Unit 8 Revision Guide Read More Unit 9 Revision Guide Read More