Chapter 24 – Chemical Reactions Section 1 – Chemical Changes

Chapter 24 – Chemical Reactions Section 1 – Chemical Changes Describing chemical reactions – change of one or more substances converted into new substances

Chapter 24 – Chemical Reactions Section 1 – Chemical Changes Describing chemical reactions – change of one or more substances converted into new substances Reactants are substances that combine or change

Chapter 24 – Chemical Reactions Section 1 – Chemical Changes Describing chemical reactions – change of one or more substances converted into new substances Reactants are substances that combine or change New substances that are produced are called products

+ -> Reactant + Reactant -> Product

Conservations of Mass – a law which states that, in a chemical reaction, matter is not created or destroyed; it stays the same

Conservations of Mass – a law which states that, in a chemical reaction, matter is not created or destroyed; it stays the same Antoine Lavoisier – experimented with mercury (II) oxide and heat

Conservations of Mass – a law which states that, in a chemical reaction, matter is not created or destroyed; it stays the same Antoine Lavoisier – experimented with mercury (II) oxide and heat Found mass of products (liquid mercury and oxygen gas) equaled mass or reactants

Writing equations – a chemical equation uses chemical formulas and symbols to describe a chemical reaction and the products it produces

Writing equations – a chemical equation uses chemical formulas and symbols to describe a chemical reaction and the products it produces Chemical formula expresses the relationship between elements in the compounds and molecules they make up

Writing equations – a chemical equation uses chemical formulas and symbols to describe a chemical reaction and the products it produces Chemical formula expresses the relationship between elements in the compounds and molecules the make up Coefficients – numbers which represent the number of units of each substance in a reaction

2 H20 coefficient = H2O + H2O

NiCl2 + 2NaOH Ni(OH)2 + 2NaCl

Knowing coefficients of chemical reactions allows chemists to use the correct amounts of reactants to predict the amounts of products

Knowing coefficients of chemical reactions allows chemists to use the correct amounts of reactants to predict the amounts of products Subscripts – numbers which represent the number of atoms in a molecule of a particular element

H20 subscript = H + H + O

Knowing coefficients of chemical reactions allows chemists to use the correct amounts of reactants to predict the amounts of products Subscripts – numbers which represent the number of atoms in a molecule of a particular element Symbols used to show state of reactants; (s) solid, (aq) aqueous [dissolved in water], (g) gas, (l) liquid

Metals react with atmosphere in different ways

Section 2 – Chemical Equations

Section 2 – Chemical Equations Checking for balance – law of conservation of mass requirement

Section 2 – Chemical Equations Checking for balance – law of conservation of mass requirement A balanced chemical reaction – both sides of equation have same number of atoms of each element

Section 2 – Chemical Equations Checking for balance – law of conservation of mass requirement A balanced chemical reaction – both sides of equation have same number of atoms of each element Choosing coefficients – becomes easier with practice; trial and error at first

2Mg(s) + O2(g) -> 2MgO(s) 2 x Mg 2 x O Fill in the missing coefficients: _____ H2(g) + O2(g) -> _____ H2O (g)

2Mg(s) + O2(g) -> 2MgO(s) 2 x Mg 2 x O Fill in the missing coefficients: __2__ H2(g) + O2(g) -> __2__ H2O (g)

Writing balanced chemical equations - a four-step process

Writing balanced chemical equations - a four-step process Describe the reaction in words

When solid sodium is placed in water it forms aqueous sodium hydroxide and hydrogen gas.

Writing balanced chemical equations - a four-step process Describe the reaction in words Write the equation using formulas and symbols

When solid sodium is placed in water it forms aqueous sodium hydroxide and hydrogen gas. Na(s) + H2O(l) -> NaOH(aq) + H2(g)

Writing balanced chemical equations - a four-step process Describe the reaction in words Write the equation using formulas and symbols Check for balance

When solid sodium is placed in water it forms aqueous sodium hydroxide and hydrogen gas. Na(s) + H2O(l) -> NaOH(aq) + H2(g) 1 x Na 1 x O 3 x H 2 x H

Writing balanced chemical equations - a four-step process Describe the reaction in words Write the equation using formulas and symbols Check for balance Add coefficients where needed for balance

Find the missing coefficients: ____ Na(s) + _____ H2O(l) -> _____ NaOH(aq) + _____ H2(g)

Find the missing coefficients: ____ Na(s) + _____ H2O(l) -> _____ NaOH(aq) + _____ H2(g) _2__ Na(s) + __2__ H2O(l) -> __2__ NaOH(aq) + __1__ H2(g)

_2__ Na(s) + __2__ H2O(l) -> __2__ NaOH(aq) + __1__ H2(g) 2 x Na 2 x O 4 x H 4 x H

Section 3 – Classifying Chemical Reactions

Section 3 – Classifying Chemical Reactions Synthesis reaction – two or more substances form a new substance; A + B -> AB

Synthesis Look for: 2 or more reactants, only one product

Section 3 – Classifying Chemical Reactions Synthesis reaction – two or more substances form a new substance; A + B -> AB One substance breaks down into two or more substances in a decomposition reaction; AB -> A + B

Decomposition Look for: only 1 reactant, 2 or more products

Section 3 – Classifying Chemical Reactions Synthesis reaction – two or more substances form a new substance; A + B -> AB One substance breaks down into two or more substances in a decomposition reaction; AB -> A + B Single-displacement reaction - one element replaces another one in a compound; A + BC -> AC + B

Single Displacement Look for: 1 compound and ion forming another compound and ion

A double-displacement reaction results if a precipitate, water, or a gas forms when ionic compounds in solution are combined; AB + CD -> AD + CB

Double Displacement Look for: 2 compounds forming 2 new compounds

Section 4 – Chemical Reactions and Energy

Section 4 – Chemical Reactions and Energy Chemical reactions involve energy exchange

Section 4 – Chemical Reactions and Energy Chemical reactions involve energy exchange Breaking chemical bonds requires energy

Section 4 – Chemical Reactions and Energy Chemical reactions involve energy exchange Breaking chemical bonds requires energy Forming chemical bonds releases energy

Section 4 – Chemical Reactions and Energy Chemical reactions involve energy exchange Breaking chemical bonds requires energy Forming chemical bonds releases energy More energy out

Exergonic reactions – energy required to break bonds is less than the energy released from new bonds; energy given off is usually light

Exergonic reactions – energy required to break bonds is less than the energy released from new bonds; energy given off is usually light Exothermic reactions – energy given off in the form of heat

Exergonic reactions – energy required to break bonds is less than the energy released from new bonds; energy given off is usually light Exothermic reactions – energy given off in the form of heat More energy in

Endergonic reactions – more energy is required to break bonds than to form new ones

Endergonic reactions – more energy is required to break bonds than to form new ones If energy needed is heat, the reaction is endothermic

Endergonic reactions – more energy is required to break bonds than to form new ones If energy needed is heat, the reaction is endothermic A catalyst speeds up a chemical reaction without itself being permanently changed

Endergonic reactions – more energy is required to break bonds than to form new ones If energy needed is heat, the reaction is endothermic A catalyst speeds up a chemical reaction without itself being permanently changed An inhibitor prevents or slows a chemical reaction or interferes with a catalyst’s action