Lectures Balancing chemical reactions Chemical Quantities and reactions

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Lectures: Balancing chemical reactions Chemical Quantities and reactions Course lecturer : Dr. Altijana Hromić-Jahjefendić

Lectures: Balancing chemical reactions Chemical Quantities and reactions Course lecturer : Dr. Altijana Hromić-Jahjefendić

� 1 mole of an element = 6. 02 x 1023 atoms of that

� 1 mole of an element = 6. 02 x 1023 atoms of that element

Moles of Elements in a Chemical Formula �Subscripts – indicate the number of atoms

Moles of Elements in a Chemical Formula �Subscripts – indicate the number of atoms of each type of element in the compound q. Example: aspirin (C 9 H 8 O 4) has 9 carbon atoms, 8 hydrogen atoms and 4 oxygen atoms �Also tells the number of moles of each element in 1 mole of aspirin � 9 moles of C atoms, 8 moles of H atoms and 4 moles of O atoms

Moles and Elements in a given formula

Moles and Elements in a given formula

Molar Mass and Calculations �Single atom or molecule is too small to weigh �It

Molar Mass and Calculations �Single atom or molecule is too small to weigh �It takes a huge number of atoms or molecules to make enough of a substance for you to see �Molar mass – quantity in grams that equals the atomic mass of that element q. Example: carbon has atomic mass of 12. 01 Ø 1 mole of carbon atoms has a mass of 12. 01 g Ø To obtain 1 mole of carbon atoms we must weigh out 12. 01 g of carbon

Calculation of true mass �M=m/n �Molar mass=mass/moles �To weight the compound

Calculation of true mass �M=m/n �Molar mass=mass/moles �To weight the compound

Equations for Chemical Reactions �Chemical change – when a substance is converted into one

Equations for Chemical Reactions �Chemical change – when a substance is converted into one or more new substances (different formulas and properties) �Example: the tarnishing of silver �Shiny silver metal (Ag) reacts with sulfur (S) �Becomes dull, black substance we know as tarnish (Ag 2 S)

�Chemical reaction – involves chemical change �Atoms of the reacting substances form new combinations

�Chemical reaction – involves chemical change �Atoms of the reacting substances form new combinations with new properties �Example: chemical reaction of iron (Fe) with oxygen (O 2) in the air �Produce a new substance Fe 2 O 3 (rust; reddish-brown color) �During chemical change new properties become visible – indicates that a chemical reaction has taken place

Writing a Chemical Equation �Chemical reaction represented by chemical equation �Example: burning charcoal in

Writing a Chemical Equation �Chemical reaction represented by chemical equation �Example: burning charcoal in a grill �Combines with oxygen to form CO 2

�In chemical equation – reactants and products �Reactants are written on the left of

�In chemical equation – reactants and products �Reactants are written on the left of the arrow and products on the right �If there are two or more formulas on the same side they are separated by plus (+) signs �Each formula is followed by physical state of the substance: solid (s), liquid (l) or gas (g). �If the substance is dissolved in water it is aqueous (aq) solution

Identifying a Balanced Chemical Equation �In chemical reaction bonds between atoms of the reactants

Identifying a Balanced Chemical Equation �In chemical reaction bonds between atoms of the reactants are broken �New bonds are formed to give the products �All atoms are conserved – atoms cannot be gained, lost or changed into other types of atoms during a chemical reaction �Every chemical reaction must be written as a balanced equation �Same number of atoms for each element in the reactants as well as in products!!!!

Balancing of Chemical Reactions �In the balanced equation there are whole numbers called coefficients

Balancing of Chemical Reactions �In the balanced equation there are whole numbers called coefficients in front of the formulas H 2 + O 2 H 2 O - unbalanced 2 H 2 + O 2 2 H 2 O - balanced

This illustrates the Law of Conservation of Matter, which states that matter cannot be

This illustrates the Law of Conservation of Matter, which states that matter cannot be created or destroyed during a chemical reaction.

Types of Reaction �A great number of reactions occur in nature �There are some

Types of Reaction �A great number of reactions occur in nature �There are some general patterns of classification

Combination �In a combination reaction, two or more elements or compounds bond to form

Combination �In a combination reaction, two or more elements or compounds bond to form one product. �Example: sulfur and oxygen combine to form the product sulfur dioxide.

Examples

Examples

Decomposition Reactions �In a decomposition reaction, a reactant splits into two or more simpler

Decomposition Reactions �In a decomposition reaction, a reactant splits into two or more simpler products. �For example, when mercury (II) oxide is heated, the compound breaks apart into mercury atoms and oxygen 2 Hg. O 2 Hg + O 2

Replacement Reactions �In a replacement reaction, elements in a compound are replaced by other

Replacement Reactions �In a replacement reaction, elements in a compound are replaced by other elements. �Single replacement reaction - reacting element switches place with an element in the other reacting compound

�In a double replacement reaction - positive ions in the reacting compounds switch places.

�In a double replacement reaction - positive ions in the reacting compounds switch places.

Combustion reactions �A carbon-containing compound (fuel) burns in oxygen from the air to produce

Combustion reactions �A carbon-containing compound (fuel) burns in oxygen from the air to produce CO 2, water or energy in the form of heat or flame q. Examples: Burning of a candle or fuel

Link to Health �Toxicity of carbon monoxide – incomplete combustion �Propane heater in a

Link to Health �Toxicity of carbon monoxide – incomplete combustion �Propane heater in a closed room – proper ventilaton �If supply of oxygen is limited – incomplete combustion from burning gas, oil or wood produces CO

Link to Health �CO (carbon monoxide) is a colorless, odorless and poisonous gas �If

Link to Health �CO (carbon monoxide) is a colorless, odorless and poisonous gas �If inhaled, passes into the bloodstream �Attaches to hemoglobin which reduces the amount of oxygen (O 2) reaching the cells �Result: person can experience a reduction in exercise capability, visual perception and other disorders

Link to Health �Hemoglobin is the protein that transports O 2 in the blood

Link to Health �Hemoglobin is the protein that transports O 2 in the blood �If amount of hemoglobin bound to CO is about 10% shortness of breath, mild headache and drowsiness �Heavy smokers can have up to 9% �If the amount is 30% - dizziness, mental confusion, severe headache �If amount is 50% or more – person could become uncounscious and die if not treated immediatelly with oxygen

Oxidation-Reduction reactions �In everyday life �Rusting (Fe is oxidized) �Turning lights in our cars

Oxidation-Reduction reactions �In everyday life �Rusting (Fe is oxidized) �Turning lights in our cars (car battery provides electicity) �Burning woods �Combustion reactions are also oxidation-reduction reaction

�Also called redox reactions �Electrons are transferred from one substance to another �One substance

�Also called redox reactions �Electrons are transferred from one substance to another �One substance loses electrons, another one gains electrons �Oxidation – loss of electrons �Reduction – gain of electrons

�Atoms of metals lose electrons to form positive ions – metals are oxidized �Nonmetals

�Atoms of metals lose electrons to form positive ions – metals are oxidized �Nonmetals gain electrons to form negative ions – nonmetals are reduced

Oxidation and Reduction in Biological Systems �In the body cells �Oxidation of organic carbon

Oxidation and Reduction in Biological Systems �In the body cells �Oxidation of organic carbon compounds involves the transfer of hydrogen atoms (protons and electrons) �Necessary for the production of energy in the cells �However, redox reactions depend on the process that occurs �But oxidation is always loss of electrons �Reduction is always gain of electrons

Balancing of chemical reactions �H 2 + O 2 → H 2 O �S

Balancing of chemical reactions �H 2 + O 2 → H 2 O �S + O 2 → SO 2 �Mg + O 2 → Mg. O �Mg. O + CO 2 → Mg. CO 3 �N 2 + H 2 → NH 3 �Hg. O → Hg + O 2 �Zn + HCl → H 2 + Zn. Cl 2 �Na. OH + HCl → H 2 O + Na. Cl �C 6 H 12 O 6 + O 2 → CO 2 + H 2 O + energy �Fe 2 S 3 + HCl → Fe. Cl 3 + H 2 S �CH 4 + O 2 → CO 2 + H 2 O

Balancing of chemical reactions �Na 3 PO 4 + Mg. Cl 2 → Mg

Balancing of chemical reactions �Na 3 PO 4 + Mg. Cl 2 → Mg 3(PO 4)2 + Na. Cl �Al + Cu. SO 4 → Al 2(SO 4)3 + Cu �K 2 SO 4 + Ba. Cl 2 → KCl + Ba. SO 4 �Sb 2 S 3 + HCl → Sb. Cl 3 + H 2 S �Zn + HNO 3 → Zn(NO 3)2 + H 2 �C 2 H 4 + O 2 → CO 2 + H 2 O + energy �Ag. NO 3 + K 2 Cr. O 4 → Ag 2 Cr. O 4 + KNO 3 �Ba(OH)2 + H 3 PO 4 → Ba 3(PO 4)2 + H 2 O �H 3 PO 4 + Na. OH → Na 3 PO 4 + H 2 O �Fe. Cl 3 + NH 4 OH → Fe(OH)3 + NH 4 Cl

Summary �Molar mass and calculations �Chemical reactions �Balancing of chemical reactions

Summary �Molar mass and calculations �Chemical reactions �Balancing of chemical reactions

Mole relationships in Chemical Equations �In any chemical reaction, the total amount of matter

Mole relationships in Chemical Equations �In any chemical reaction, the total amount of matter in the reactants is equal to the total amount of matter in the products. �Thus, the total mass of all the reactants must be equal to the total mass of all the products �Known as the law of conservation of mass, which states that there is no change in the total mass of the substances reacting in a chemical reaction.

q. Example: tarnish (Ag 2 S) forms when silver reacts with sulfur from silver

q. Example: tarnish (Ag 2 S) forms when silver reacts with sulfur from silver sulfide �In this reaction the number of silver atoms is twice the number of sulfur atoms

Energy in Chemical Reactions �Molecules of the reactants must collide with each other, have

Energy in Chemical Reactions �Molecules of the reactants must collide with each other, have proper orientation and energy �Sufficient energy to break the bonds of the reactants �Activation energy – amount of energy required to break the bonds between atoms

Energy in Chemical Reactions Three Conditions Required for a Reaction to Occur � 1.

Energy in Chemical Reactions Three Conditions Required for a Reaction to Occur � 1. Collision - The reactants must collide. � 2. Orientation - The reactants must align properly to break and form bonds. � 3. Energy - The collision must provide the energy of activation.

Exothermic Reactions �Heat is absorbed or released as reactants convert to the products �In

Exothermic Reactions �Heat is absorbed or released as reactants convert to the products �In exothermic reaction – energy of the products is lower that the energy of the reactants �Heat is released in exothermic reactions

Endothermic reactions �The energy of the products is higher than of the reactants �Heat

Endothermic reactions �The energy of the products is higher than of the reactants �Heat is absorbed in endothermic reactions

Chemistry Link to Health �First-aid station: cold pack �Reduces swelling from an injury, removes

Chemistry Link to Health �First-aid station: cold pack �Reduces swelling from an injury, removes heat from inflammation �Inside of cold pack is solid ammonium nitrate separated from the compartment containig water �Activation: hiting or squeezing to break the walls and mix nitrate with water

Chemistry to Health �Hot packs �Contain salt Ca. Cl 2 �When 1 mole of

Chemistry to Health �Hot packs �Contain salt Ca. Cl 2 �When 1 mole of Ca. Cl 2 dissolves in water, energy is released as heat �The temperature rises to almost 66 °C and can be used

Rate of Reaction �The rate (speed) is measured by: - the amount of reactant

Rate of Reaction �The rate (speed) is measured by: - the amount of reactant used up - the amount of product formed �In a certain period of time �The rate is affected by: - Changes in temperature - Changes in the concentration of the reactants - Addition of catalysts

Temperature �Higher temperatures – increase in kinetic energy makes reactants move faster and collide

Temperature �Higher temperatures – increase in kinetic energy makes reactants move faster and collide often �Higher temperatures – faster reactions q. Example: cooking �Lower temperatures – slower reactions q. Example: in cardiac surgery, body temperature is lowered to 28 °C so the heart can be stopped and less oxygen is required by the brain �The reason why some people survived submersion in icy lakes for longer period

Concentrations of Reactants �Adding reactants – increasing the rate of reaction �More collisions between

Concentrations of Reactants �Adding reactants – increasing the rate of reaction �More collisions between the reactants -> reaction faster q. Example: patient with difficulty breathing may be given a mixture with a higher oxygen contant �The increase in the number of oxygen molecules in the lungs – increases the rate at which oxygen combines with hemoglobin

Catalysts �To speed up a reaction – lower the energy of activation �Adding catalyst

Catalysts �To speed up a reaction – lower the energy of activation �Adding catalyst �Provides alternate pathway with a lower energy requirenment �Result: more collisions form product successfully �Many uses in industry (margarine production speed up with platinum) �In body – enzymes �Make most metabolic reactions go at the rates needed for proper cellular activity

Summary �Types of reactions �Redox reactions �Mole relationships in chemical equations �Mass calculations for

Summary �Types of reactions �Redox reactions �Mole relationships in chemical equations �Mass calculations for reactions �Energy in chemical reactions �Rate of reactions

Assignment �Calculate the mass in grams for following compounds: Ø 1. 75 moles of

Assignment �Calculate the mass in grams for following compounds: Ø 1. 75 moles of C 19 H 20 FNO 3 Ø 4. 42 moles of C 4 H 8 O 4 Ø 2 moles of Ga 2(CO 3)2 Ø 5 moles of Al 2(SO 4)3 Ø 0. 5 moles of Mg(OH)2 Ø 3. 75 moles of Fe 2 O 3 Ø M=m/n