5 Chemical - Kossmann-Greenall · PDF fileChemical Equation: 2 C8H12 + 25 O2 16 CO2 + 18 H2O. 5 Chemical reactions ... + Ba(OH)2 (aq) → ... 5 Chemical October 18, 2016

5 Chemical reactions.notebook October 18, 2016

Chemical Reactions

Evidence of a Chemical Reaction

A new substance is formed...

Colour changeEnergy Change (heat and Light)Bubbles (gas formed)Precipitate (solid out of solution)


There are three ways to represent a chemical reaction

1. The Word Equation only the chemical names and states of the reactants and products are shown.

Solid (s)Liquid (usually water, H2O) – (l)Gas (g) Dissolved in water (aq)

2. The Skeletal Equation The chemical formulas for the reactants and products are shown.

3. The Chemical Equation the proportions of reactants and products are shown with coefficients in front of the chemical symbols for each substance.

Eample: The word equation and chemical equation for the combustion of octane:

Word Equation:

Octane(l) + Oxygen(g) Carbon Dioxide(g) + water(l)Skeletal Equation: C8H12 + O2 CO2 + H2O

Chemical Equation: 2 C8H12 + 25 O2 16 CO2 + 18 H2O


Solid Sodium bicarbonate reacts with Hydrochloric acid to produce aqueous sodium chloride, liquid water and gaseous carbon dioxide.

5 Types of Chemical Reactions

Synthesis (combination)Decomposition

Single replacement (displacement)Double replacement (displacement)

Combustion

We can use our knowledge of how compounds form and the types of reactions to predict the out comes of different reactions


Synthesis (Combination) ReactionsTwo or more simple substances combine to form a more complex compound.

A + B AB

bird + worm fat bird

C (s) + O2 (g) → CO2 (s)

Practice: Complete and balance the following combinations reactions:

K (s) + Cl2 (g) → Li (s) + Br2 (l) →

Mg (s) + N2 (g) →

Be (s) + O2 (g) →

SO2 (g) + H2O (l) →

CaO (s) + H2O (l) →

Li2O (s) + CO2 (g) →


Decomposition Reaction

This is just the opposite of a combination reaction

One substance breaks down to form 2 or more simpler substances

AB A + B

Cracking egg Broken egg + turtle

2 HgO (s) → 2 Hg (l) + O2 (g)

Rules for Decomposition Reactions!

Most decomposition reaction occur when the chemical is heated (but not burned)

1. If there are only two elements in the compound the reaction will decompose into elementsThis is rare!

2. Acids break down into water and a basic (metal) oxide

3. Bases break down into water and an acidic (nonmetal) oxide

4. Carbonates break down into an oxide and carbon dioxide

5. Sulfates break down into an oxide and sulfur trioxide

6. Chlorates break down into a chloride and oxygen


Practice: Complete and balance the following decomposition reactions: AgCl (s) → MgCO3 (s) → Mg(OH)2 (s) → CsI (s) → Sr(ClO3)2 (s) → FeSO4 (s) → H2SO4 (aq) →

One element replaces another in a compound

A + BC → AC + B OR AB + C → AC + B

girl and Guy + Girl → Girl and Guy + girl

Cl2 (aq) + 2 NaBr (aq) → Br2 (aq) + 2 NaCl (aq)

Single Replacement Reactions


Practice: Complete and balance the following replacement reactions:

Zn (s) + NiCl2 (aq) →

I2 (aq) + KF (aq) →

Cu (s) + AgNO3 (aq) →

Cl2 (aq) + NaI (aq)→

Ca (s) + H2O (l) →

Zn (s) + CuCl2 (aq) →

Br2 (aq) + CaCl2 (aq) →

Al (s) + H2SO4 (aq) →

H2 (g) + AgNO3 (aq) →

AuN (aq) + Ca (s) →

Double Replacement Reactions

Always involves two ionic compounds Symbolized as:

AB + CD → AD + CB

girl and Guy + Girl and guy → Girl and Guy + girl and guy

CaCl (s) → 2 Hg (l) + O2 (g)


Practice: Complete and balance the following double replacement reactions:

AgNO3 (aq) + NaI (aq) →

MgSO4 (aq) + NaOH (aq) →

(NH4)2SO4 (aq) + KOH (aq) →

K2CO3 (aq) + HNO3 (aq)→

Na2S (aq) + K2SO4 (aq) →

H2SO4 (aq) + LiOH (aq) →

BaCl2 (aq) + AgNO3 (aq) →

Fe(NO3)3 (aq) + LiOH (aq) →

HCL (aq) + Ba(OH)2 (aq) →

Combustion ReactionsUsually gives off a large amount of energy in the form of heat and light. Involves the reaction of a substance with oxygen. Otherwise known as burning.

Hydrocarbons (hydrogen and carbon) BurningAlways has water and carbon dioxide as a product. Ex propane, gasoline, fuel, oil, natural gas

Other SubstancesSubstances other than hydrocarbons will burn in oxygen. For example, the combustion of magnesium to form magnesium oxide is usually conducted in the presence of oxygen.

2Mg + O 2 2MgO

You may notice that this equation looks like a synthesis equation. In fact, it can be described as either a synthesis or combustion. Many reactions you encounter can actually be classified several ways.

CxHy + O2 CO 2 + H2O


Practice: Write out the balanced chemical equations for the combustion of:MethaneEthane Propane Butane Pentane Hexane Heptane Octane Nonane Decane C6H12O6 + O2 →

Acid Base Reduction ReactionsA special type of double replacement reaction is the Acid Base Reduction. In this reaction the acid and base react to form water and some salt (ide).

HCl + NaOH NaCl + H2O


GUMMY Sacrifice

2NaClO3(s) + heat 2NaCl(s) + 3O2(g)

Step 1:

Step 2: C12H22O11(s) + 3O2(g) 9C(s) + 3CO2(g)

+11H2O(g) + 5635kJ(Sugar)

Is this an exothermic or endothermic reaction?

How do you know?

What is happening inside the system?

What is occurring around the system?

Write this equation with the heat as a ΔQ separate from the balanced chemical equation.

Write a word equation for this reaction.

Write a balanced chemical equation for the reverse reaction.

What will this decompose into?


Ba(OH)2 8H2O(s) + 2NH4SCN(s) + heat Ba(SCN)2(aq) + 2NH3(aq) +10H2O(l)

What do you notice?

What is occurring in the surroundings and the system during the reaction?

Do the reactants contain low or high energy bonds relative to the products? Explain.

Is this an endothermic or exothermic reaction? How do you know?

If 15,000 molecule of H2O are produced:(a) how many molecules of ammonium thiocyanate were reacted?

(b) how many molecules of ammonia gas would be produced?

Types of chemical reactions - Matching

Synthesis

Decomposition

Combustion

A chemical reaction in which two or more substances react to produce a single product.

A+B ABCaO(s) + H2O(l) Ca(OH)2(s)

2SO2(g) + O2(g) 2SO3(g)

A chemical reaction in which oxygen combines with a substance (fuel) and releases energy in the form of heat or light. Carbon dioxide gas and water vapor are typical products of this type of reaction.

2SO2(g) + O2(g) 2SO3(g)

Solid aluminum and solid sulfur react to produce aluminum sulfide.

Liquid water and dinitrogen pentaoxide gas react to produce aqueous nitric acid.

Nickel (II) hydroxide breaks down into Nickel (II) oxide and water.

A chemical reaction in which two or more substances react to produce a single product.

AB A + B

AB B + A + heat

B+A+ heat AB

The two ways of representing exothermic reactions are shown below....1. 2. The two ways of

representing endothermic reactions are shown below....1. 2.

If 4NO(g) + 6H2O(g) + 904.68kJà 4NH3(g) + 5O2(g) Then, reacting 18 NO(g) molecules would

require __________ kJ of energy.

If 4NH3(g) + 5O2(g) à 4NO(g) + 6H2O(g) + 904.68kJThen, producing 18 H2O(g) molecules would

produce __________ kJ of energy. Additional Info....

Additional Info....

Additional Info....

Help... My binder fell open and all the ideas in this unit are scattered and some pieces are lost.... Help me put this unit back together...!!!


Exam

EXOTHERMIC AND ENDOTHERMIC REACTIONS

A B B

BA +B

LOW energybonds

HIGH energybonds

EXOTHERMIC

A B B

BA +B

ENDOTHERMIC

LOW energybonds

HIGH energybonds

HIGH energybonds

LOW energybonds

SUMMARY:

For exothermic reactions...

Energy is produced in a chemical process (energy is a product)!

H is negative

Heat moves into the system from the surroundings

HEATSystem

When you break the pack of Barium hydroxide octahydrate (in the middle), it mixes and begins to react with the ammonium cyanide. Energy (in the form of heat) is absorbed from the surroundings making the surroundings feel cool.

For endothermic reactions...

Energy is required in a chemical process (energy is a reactant)!

H is positive

HEATSystem

Heat moves out of the system to the surroundings

In thermodynamics, a system is defined as that part of the universe that is under consideration, what we are examining.




ENDOTHERMIC REACTIONS

EXOTHERMIC REACTIONS

2H2(g) + O2(g) à 2H2O(l) + 484KJ 2H2(g) + O2(g) à 2H2O(l) ∆H= 484KJ

OR4H2O(l) + 968KJ à 4H2(g) + 2O2(g)

OR

4H2O(l) à 4H2(g) + 2O2(g) ∆H= + 968KJ

What do you notice?

Problem Set #2 questions

Reversing chemical equations....If it requires 2.2kJ of energy to evaporate 2 water molecules, how much energy would be released if 2 water molecules condensed?

Summary....


Changing quantities in chemical equations....If it requires 2.2kJ of energy to evaporate 2 water molecules, how much energy would be required if 17 water molecules were to evaporate?

Summary....

teacher notes for reaction:Solid barium hydroxide octahydrate (Ba(OH)2

.8H2O) and ammonium thiocyanate (NH4SCN) are mixed in a beaker, which is then placed on a few drops of water on a small board. The reaction that occurs is highly endothermic, and it causes the beaker to freeze to the board. The low temperature (below 0 oC) is read by a digital thermometer. The gas produced by the reaction is shown to be basic by the use of pH paper. The equation for the reaction is given.

32g Barium Hydroxide octahydrate: 17g Ammonium thiocyanate. 4g : 2.2g

Perform the Demonstration • Pour the barium hydroxide and ammonium thiocyanate into the flask. • Stir the mixture. • The odor of ammonium should become evident within about 30 seconds. If you hold a piece of dampened litmus paper over the reaction you can watch a color change showing that the gas produced by the reaction is basic. • Liquid will be produced, which will freeze into a slush as the reaction proceeds. • If you set the flask on a damp block of wood or piece of cardboard while performing the reaction you can freeze the bottom of the flask to the wood or paper. You can touch the outside of the flask, but don't hold it in your hand while performing the reaction. • After the demonstration is completed, the contents of the flask can be washed down the drain with water. Do not drink the contents of the flask. Avoid skin contact. If you get any solution on your skin, rinse it off with water.

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5 Chemical - Kossmann-Greenall · PDF fileChemical Equation: 2 C8H12 + 25 O2 16 CO2 + 18 H2O. 5 Chemical reactions ... + Ba(OH)2 (aq) → ... 5 Chemical October 18, 2016