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Chemical Reactions: An Introduction

chemical Reakction "An Introduction" reaksi kimia

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Page 1: chemical Reakction "An Introduction" reaksi kimia

Chemical Reactions:An Introduction

Page 2: chemical Reakction "An Introduction" reaksi kimia

Chemical Reactions• Reactions involve chemical changes in

matter resulting in new substances• Reactions involve rearrangement and

exchange of atoms to produce new molecules– Elements are not transmuted during a reaction

Reactants Products

Page 3: chemical Reakction "An Introduction" reaksi kimia

Evidence of Chemical Reactions

• a chemical change occurs when new substances are made

• visual clues (permanent)– color change, precipitate formation, gas

bubbles, flames, heat release, cooling, light• other clues

– new odor, permanent new state

Page 4: chemical Reakction "An Introduction" reaksi kimia
Page 5: chemical Reakction "An Introduction" reaksi kimia

Chemical Equations

• Shorthand way of describing a reaction• Provides information about the reaction

– Formulas of reactants and products– States of reactants and products– Relative numbers of reactant and product

molecules that are required– Can be used to determine weights of

reactants used and of products that can be made

Page 6: chemical Reakction "An Introduction" reaksi kimia

Conservation of Mass

• Matter cannot be created or destroyed• In a chemical reaction, all the atoms

present at the beginning are still present at the end

• Therefore the total mass cannot change• Therefore the total mass of the reactants

will be the same as the total mass of the products

Page 7: chemical Reakction "An Introduction" reaksi kimia

Combustion of Methane

• methane gas burns to produce carbon dioxide gas and liquid water– whenever something burns it combines with O2(g)

CH4(g) + O2(g) CO2(g) + H2O(l)

H

HC

H

HOO+

O

O

C + OH H

1 C + 4 H + 2 O 1 C + 2 O + 2 H + O1 C + 2 H + 3 O

Page 8: chemical Reakction "An Introduction" reaksi kimia

Combustion of MethaneBalanced

• to show the reaction obeys the Law of Conservation of Mass it must be balanced

CH4(g) + 2 O2(g) CO2(g) + 2 H2O(l)

H

HC

H

H

OO+

O

O

C +O

H H

OO+

OH H

+

1 C + 4 H + 4 O 1 C + 4 H + 4 O

Page 9: chemical Reakction "An Introduction" reaksi kimia

Writing Equations• Use proper formulas for each reactant and product• proper equation should be balanced

– obey Law of Conservation of Mass– all elements on reactants side also on product side– equal numbers of atoms of each element on reactant

side as on product side• balanced equation shows the relationship between

the relative numbers of molecules of reactants and products – can be used to determine mass relationships

Page 10: chemical Reakction "An Introduction" reaksi kimia

Symbols Used in Equations

• symbols used after chemical formula to indicate state– (g) = gas; (l) = liquid; (s) = solid– (aq) = aqueous, dissolved in water

Page 11: chemical Reakction "An Introduction" reaksi kimia

Sample – Recognizing Reactants and Products

• when magnesium metal burns in air it produces a white, powdery compound magnesium oxide– burning in air means reacting with O2

– Metals are solids, except for Hg which is liquid write the equation in words

– identify the state of each chemicalmagnesium(s) + oxygen(g) magnesium oxide(s)

write the equation in formulas– identify diatomic elements– identify polyatomic ions– determine formulas

Mg(s) + O2(g) MgO(s)

Page 12: chemical Reakction "An Introduction" reaksi kimia

Balancing by Inspection Count atoms of each element

a polyatomic ions may be counted as one “element” if it does not change in the reaction

Al + FeSO4 Al2(SO4)3 + Fe1 SO4 3

b if an element appears in more than one compound on the same side, count each separately and add

CO + O2 CO2

1 + 2 O 2

Page 13: chemical Reakction "An Introduction" reaksi kimia

Balancing by Inspection• Pick an element to balance

• avoid elements from 1b• Find Least Common Multiple and factors

needed to make both sides equal• Use factors as coefficients in equation

• if already a coefficient then multiply by new factor

• Recount and Repeat until balanced

Page 14: chemical Reakction "An Introduction" reaksi kimia

Examples• when magnesium metal burns in air it produces

a white, powdery compound magnesium oxide– burning in air means reacting with O2

write the equation in words– identify the state of each chemicalmagnesium(s) + oxygen(g) magnesium oxide(s)

write the equation in formulas– identify diatomic elements– identify polyatomic ions– determine formulas

Mg(s) + O2(g) MgO(s)

Page 15: chemical Reakction "An Introduction" reaksi kimia

Examples• when magnesium metal burns in air it produces

a white, powdery compound magnesium oxide– burning in air means reacting with O2

count the number of atoms of on each side– count polyatomic groups as one “element” if on both

sides– split count of element if in more than one compound

on one side

Mg(s) + O2(g) MgO(s)

1 Mg 1 2 O 1

Page 16: chemical Reakction "An Introduction" reaksi kimia

Examples• when magnesium metal burns in air it produces

a white, powdery compound magnesium oxide– burning in air means reacting with O2

pick an element to balance– avoid element in multiple compounds

° find least common multiple of both sides & multiply each side by factor so it equals LCM

Mg(s) + O2(g) MgO(s)

1 Mg 1 1 x 2 O 1 x 2

Page 17: chemical Reakction "An Introduction" reaksi kimia

Examples• when magnesium metal burns in air it

produces a white, powdery compound magnesium oxide– burning in air means reacting with O2

± use factors as coefficients in front of compound containing the element if coefficient already there, multiply them together

Mg(s) + O2(g) 2 MgO(s)

1 Mg 1 1 x 2 O 1 x 2

Page 18: chemical Reakction "An Introduction" reaksi kimia

Examples• when magnesium metal burns in air it produces

a white, powdery compound magnesium oxide– burning in air means reacting with O2

Recount

Mg(s) + O2(g) 2 MgO(s) 1 Mg 2

2 O 2 Repeat

2 Mg(s) + O2(g) 2 MgO(s) 2 x 1 Mg 2

2 O 2

Page 19: chemical Reakction "An Introduction" reaksi kimia

Examples• Under appropriate conditions at 1000°C ammonia gas

reacts with oxygen gas to produce gaseous nitrogen monoxide and gaseous water

• write the equation in words– identify the state of each chemical

ammonia(g) + oxygen(g) nitrogen monoxide(g) + water(g) write the equation in formulas

– identify diatomic elements– identify polyatomic ions– determine formulas

NH3(g) + O2(g) NO(g) + H2O(g)

Page 20: chemical Reakction "An Introduction" reaksi kimia

Examples• Under appropriate conditions at 1000°C ammonia gas

reacts with oxygen gas to produce gaseous nitrogen monoxide and gaseous water

count the number of atoms of on each side– count polyatomic groups as one “element” if on both

sides– split count of element if in more than one compound on

one side

NH3(g) + O2(g) NO(g) + H2O(g)

1 N 13 H 2

2 O 1 + 1

Page 21: chemical Reakction "An Introduction" reaksi kimia

Examples• Under appropriate conditions at 1000°C ammonia

gas reacts with oxygen gas to produce gaseous nitrogen monoxide and gaseous water

pick an element to balance– avoid element in multiple compounds

° find least common multiple of both sides & multiply each side by factor so it equals LCM

NH3(g) + O2(g) NO(g) + H2O(g)1 N 1

2 x 3 H 2 x 3 2 O 1 + 1

Page 22: chemical Reakction "An Introduction" reaksi kimia

Examples• Under appropriate conditions at 1000°C

ammonia gas reacts with oxygen gas to produce gaseous nitrogen monoxide and gaseous water

± use factors as coefficients in front of compound containing the element

2 NH3(g) + O2(g) NO(g) + 3 H2O(g)

1 N 12 x 3 H 2 x 3 2 O 1 + 1

Page 23: chemical Reakction "An Introduction" reaksi kimia

Examples• Under appropriate conditions at 1000°C ammonia gas

reacts with oxygen gas to produce gaseous nitrogen monoxide and gaseous water

Recount2 NH3(g) + O2(g) NO(g) + 3 H2O(g)

2 N 16 H 6

2 O 1 + 3 Repeat

2 NH3(g) + O2(g) 2 NO(g) + 3 H2O(g) 2 N 1 x 2

6 H 6 2 O 1 + 3

Page 24: chemical Reakction "An Introduction" reaksi kimia

Examples• Under appropriate conditions at 1000°C

ammonia gas reacts with oxygen gas to produce gaseous nitrogen monoxide and gaseous water

´ Recount2 NH3(g) + O2(g) 2 NO(g) + 3 H2O(g)

2 N 26 H 6

2 O 2 + 3

Page 25: chemical Reakction "An Introduction" reaksi kimia

Examples• Under appropriate conditions at 1000°C ammonia gas

reacts with oxygen gas to produce gaseous nitrogen monoxide and gaseous water

Repeat– A trick of the trade, when you are forced to attack an element that is

in 3 or more compounds – find where it is uncombined. You can find a factor to make it any amount you want, even if that factor is a fraction!

– We want to make the O on the left equal 5, therefore we will multiply it by 2.5

2 NH3(g) + 2.5 O2(g) 2 NO(g) + 3 H2O(g)

2 N 26 H 6

2.5 x 2 O 2 + 3