What are changes in matter? Chemical changes

What are changes in matter? There are three types of changes:  Physical changes (ice melting)  Chemical changes (wood burning)  Nuclear changes (uranium reacting in a nuclear reactor)

Physical Changes Difference between characteristic properties and non- characteristic properties: Characteristic properties help to identify a substance. Example: melting point. Non-characteristic properties help to describe a substance. Example: mass. In a physical change, characteristic properties do not change. Only the shape or the states of matter (solid, liquid, gas) can be changed.

Definition A physical change alters neither the nature nor the characteristic properties of matter. The atoms and molecules of the substance do not change. Example: boiling water (only the state of matter changes from liquid to gas).

Chemical Changes Characteristic properties will change in a chemical change because a new substance will be formed. The atoms will make different bonds which will lead to different molecules. Definition: a chemical change alters the nature and characteristic properties of matter. The bonds between atoms are rearranged, and new molecules are formed.

Chemical Changes Example: wood burning  ash is formed = new substance.

Reactants becoming Products When substances change and form new ones as bonds are broken and rearranged, the change occurs gradually.

Some signs that a chemical change occurred A) the release of gas B) the emission or absorption of heat C) the emission of light D) a change in color E) the formation of a precipitate

How to write chemical changes or chemical reactions CH 4(g) + 2O 2(g)  CO 2(g) + 2H 2 O (g) Methane reacts with oxygen to form carbon dioxide and water vapour Symbols used:  = the arrow means “forms” or “yields” + = the plus sign on the reactants side means “reacts with” and on the products sign means “and”. (g) = gas (s) = solid (l) = liquid (aq) = aqueous (dissolved in water)

The Law of Conservation of Mass Definition: the total mass of reactants is always equal to the total mass of products. Nothing is lost, nothing is created, everything is transformed. Paper burning: the mass of the gases released in the combustion and the mass of the ashes is equal to the mass of the paper in its original form. The bonds between the reactants change.

? Visualizing a Chemical Reaction Na + Cl 2 NaCl ___ mole Cl 2 ___ mole NaCl___ mole Na

Balancing chemical equations To follow the law of conservation of matter, we must balance chemical equations. Definition: balancing chemical equations consists in placing a coefficient before each reactant and product so that the number of atoms of each element on the reactant side is equal to the number of atoms of each element on the product side.

Meaning of Coefficients 2 Na + Cl 2 2 NaCl 2 g sodium1 g chlorine2 g sodium chloride + = 2 mol sodium1 mol chlorine2 mol sodium chloride (2 mol Na) x (23 g/mol) (1 mol Cl 2 ) x (71 g/mol) (2 mol NaCl) x (58.5 g/mol) 46 g71 g 117 g 2 atoms Na1 molecule Cl 2 2 molecules NaCl

Meaning of Chemical Formula Chemical Symbol Meaning Composition H 2 O One molecule of water: Two H atoms and one O atom 2 H 2 O Two molecules of water: Four H atoms and two O atoms H 2 O 2 One molecule of hydrogen peroxide: Two H atoms and two O atoms

Balancing Equations Rules Coefficients must be whole numbers. Coefficients must be as small as possible. New substances must never be added, nor existing substances removed. Subscripts in chemical formulas must never be changed. The final equation should always be checked by counting the number of atoms of each element on both sides.

Balancing Equations: same number of atoms in reactants and products N 2 + 3H 2  2NH 3 Is this formula balanced? How many atoms of N 2 ? 4FeS O 2  2 Fe 2 O SO 2 Is this formula balanced? How many moles of O 2 ? CH 4 + O 2  CO 2 + H 2 O Is this formula balanced?

How molecules are symbolized Cl 2 2Cl 2Cl 2 Molecules may also have brackets to indicate numbers of atoms. E.g. Ca(OH) 2 O H O H Ca Notice that the OH is a group The 2 refers to both H and O How many of each atom are in the following? a) NaOH b) Ca(OH) 2 c) 3Ca(OH) 2 Na = 1, O = 1, H = 1 Ca = 1, O = 2, H = 2 Ca = 3, O = 6, H = 6

Balancing equations: MgO Example: Magnesium + Oxygen Mg + O 2  MgO O MgO +  O However, this is not balanced Left: Mg = 1, O = 2 Right: Mg = 1, O = 1

a)KNO 3  KNO 2 + O 2 b)Pb(NO 3 ) 2  PbO + NO 2 + O 2 c)P 4 + I 2  PI 3 d)MgO + H 3 PO 4  Mg 3 (PO 4 ) 2 + H 2 O e)Br 2 + KI  I 2 + KBr f)Ca(OH) 2 + HNO 3  Ca(NO 3 ) 2 + H 2 O g) Bi 2 O 3 + H 2  Bi + H 2 O h)Fe + O 2  Fe 3 O 4 i)CaO + C  CaC 2 + CO 2 Here are some more to balance:

a)2KNO 3  2KNO 2 + O 2 b)2Pb(NO 3 ) 2  2PbO + 4NO 2 + O 2 c)P 4 + 6I 2  4PI 3 d)3MgO + 2H 3 PO 4  Mg 3 (PO 4 ) 2 + 3H 2 O e)Br 2 + 2KI  I 2 + 2KBr f)Ca(OH) 2 + 2HNO 3  Ca(NO 3 ) 2 + 2H 2 O g) Bi 2 O 3 + 3H 2  2Bi + 3H 2 O h)3Fe + 2O 2  Fe 3 O 4 i)2CaO + 5C  2CaC 2 + CO 2 Here are some more to balance:

Cl H H H HH H H H 2 + Cl 2  HCl H 2 + Cl 2  2 HCl reactants products H Cl reactants products H Cl (unbalanced) (balanced) Unbalanced and Balanced Equations

Types of Chemical Change Acid-base neutralization Combustion Cellular respiration and photosynthesis

Acid-Base Neutralization Definition: a chemical change involving the reaction of an acid with a base, producing a salt (metallic ion and non- metallic ion) and water. acid(aq) + base(aq)  salt(aq) + water(l) When a solution is neutralized, the concentration of H+ ions is equal to that of OH- ions and the pH is 7. If there are more H+ ions than OH- ions, the neutralization reaction is incomplete and the pH is less than 7. If there are more OH- ions than H+ ions, the neutralization reaction is incomplete and the pH is more than 7.

Neutralization HCl + NaOH → H 2 O + NaCl acidbase water salt

Combustion To understand combustion, we must first know the meaning of oxidation. Oxidation is a chemical reaction involving oxygen or a substance with properties similar to those of oxygen. Humidity accelerates the formation of rust = an oxidation of iron. Definition: Combustion is a form of oxidation that releases a large amount of energy.

Combustion Requirements

The triangle of fire A) oxidizing agent: aka oxidant, is a substance that can cause a fuel to react. Oxygen is the most common oxidant on Earth. B) A fuel is a substance that releases a large amount of energy by reacting with an oxidizing agent. E.g. wood and propane. C) the ignition temperature is the minimum temperature at which the energy present is sufficient to start combustion (they vary according to fuel types).

3 types of combustion 1. Rapid combustion Lots of energy (mostly heat and light) is released within a short period of time. E.g. log fire, candle 2. Spontaneous combustion Fast combustion with no extra source of energy for the ignition temperature. Forest fires = very hot summer and very dry ground, wood can catch fire spontaneously. 3. Slow combustion Very long period of time, energy released gradually into the environment. E.g. metal corrosion, cellular respiration.

Cellular Respiration and Photosynthesis Cellular respiration takes place in the cells of most living organisms. Definition: chemical change in which glucose and oxygen are used to generate energy. The reaction also produces carbon dioxide and water. Photosynthesis is the opposite reaction. Plant cells use solar energy to make their own glucose and oxygen by using water and carbon dioxide. Definition: chemical change that produces glucose and oxygen from solar energy, carbon dioxide and water.

Cellular respiration and photosynthesis Organisms that carry out photosynthesis are called producers because its product is used by other living organisms to survive.

Nuclear Transformation In this type of change, the atom is changed at its core – the nucleus. In uranium reactors, the nucleus is split and new substances are formed (krypton and barium).