Science Second Quarter

Cooking

• simplest and most accessible form of chemistry

• involves transformation of diff ingredients to create new products through chem reactions

chemical reactions

• one or more substances are transformed into one or more diff substances through breaking and forming chem bonds

• results in change of composition and properties

• takes place if there’s chem change

• irreversible

chemical

any form of matter w/ a definite composition and properties

reaction

any response/change that occurs as a result of an action/event

events of chem reactions

1. chem bond breaks

2. atoms of broken compound rearrange

3. new chem bonds formed

4. new compounds produced

signs of chem reaction

• change in color

• change in odor

• light emission

• change in temp

• production of gas

• change in pH

• precipitate formation

change in color

• noticeable change can indicate chem reaction

• ex: iron rusts: metallic gray → reddish brown

iron rusts

bcs of oxygen

change in odor

• new/diff odor paired w/ change of taste can be chem reaction sign

• ex: rotting food → bad odor

light emission

• some reactions produce light (may be glow or flash)

• ex: magnesium combusts in fireworks → bright white light

change in temp

• reaction may release heat (exothermic) or absorb heat (endothermic) causing temp increase/decrease

• ex: baking cake absorbs heat → expands cake components

endothermic reaction

• reaction absorbs energy from surrounding

• increase temp of materials involved

• heat in surroundings → object

endothermic reaction ex

• cooking veggies

• breaking bond → softer

exothermic reaction

• reaction releases energy through heat to surroundings

• increase temp in surrounding area of reaction

• heat exits object → surroundings

• ex: making ice cube

production of gas

• gas formation (often observed as bubbles, fizzing, steam, or smoke) indicates chem reaction

• ex: baking soda + vinegar → carbon dioxide produced

change in pH

• change in acidity/basicity can signal chem reaction

• ex: kimchi fermentation → increase acidity

precipitate formation

• occurs when product of a reaction is insoluble in the solvent causing it to come out of the solution as a solid

• ex: NaCl + AgNO₃ = AgCl (precipitate)

precipitate

solid that forms and separates from a liquid solution as result of a chem reaction

components of chem reaction

• reactant

• product

reactant

• starting substances/ingredients in chem reaction

• undergo changes to form new substances

product

• substances formed as a result of chem reaction

• new compounds that result from rearrangement of atoms in reactants

chem reaction ex

oxygen gas + hydrogen gas (reactants) = Dihydrogen monoxide (product)

pH

• presence of Hydrogen

• 1-14 scale

• 7 neutral (water)

• above 7 - basic

• below 7 - acidic

collision theory

• states that colliding particles must collide w/ one another in a chem reax ← collide, w/ sufficient energy, w/ proper orientation

• rate of collision and interaction increase = chem reax increase

factors affecting chem reactions

• temp

• amt of substance/reactant

• surface area

• nature of reactants

• presence of catalyst

temp

• particles gain KE, move faster and collide more w/ greater energy leading to faster reactions and vice versa

• ex: increased temp = cooking food faster, decreased temp = refrigeration

increased temp

molecules move faster → more collisions → faster reactions

decreased temp

molecules move slower → less collisions → slower reactions

amt of substance/reactant

• no. of collisions between reactant molecules increases as amt/concentration increases

• increased concentration = faster reaction

amt of substance/reactant ex

• how to increase fire intensity - increase amt of fuel, ignition, o2

• how to increase food production - increase amt of ingredients

surface area

• total area of exposed outer surface of a 3d object

• more particles of solid reactant exposed to other reactants = faster reaction

• increases surface area = faster reaction

• more surface area, less size, more reaction and vise versa

surface area ex

• why are some medicines better as chewables - chewing → more surface area → faster reaction

• which rusts faster 1kg of nails or 1kg of solid iron- 1kg of nails bcs more surface area to rust

nature of reactants

• physical or chemical state w/ innate characteristics

• ex: which burns faster coal or gasoline? - gasoline bcs it’s a liquid → evaporate → mix easier w/ o2 in air

physical state

• matter (solid, liquid, gas), melting and boiling pts, weight, mass

• fastest reaction: gasses(confined in small space) → liquids → solids

chemical structure

ionic compounds react faster than covalent bcs their bonds are easier to break

presence of catalyst

• substance that speeds up rate of chem reax w/o being consumed/permanently altered in process

• catalysts reduce barrier reactants need to overcome, increasing # of successful collisions

• Catalysts never present/involved in end product, only there as support

presence of catalyst ex

• enzymes - biological catalysts

• platinum - automotive catalytic converter

• nickel - catalyst in hydrogenation (oil→margarine)

• sodium bicarbonate - baking soda, leavening agent, decomposes → co2

Enzymes

• amylase - breaks down starches to sugar

• lipase - breaks down fats to fatty acids and glycerol

effect of catalyst on chem reax

• cfcs catalyze breakdown of ozone, single cl atom can catalyze thousands of ozone molecules into o2

• production of ammonia using an iron catalyst

chemical equations

• visual rep of chem reax

• only + sign used, no others

• = sign replaced w/ →

• 2 components, reactants(tail of arrow) and products(arrowhead)

• coefficients and subscripts used

• basic ex: 2H₂(g)+O₂(g)→2H₂O(g)

State symbols

• (s)

• (l)

• (g)

• (aq) - dissolved in water

Types of chem reactions

• combination reaction

• decomposition reaction

• single displacement reaction

• double displacement reaction

• combustion reaction

combination reaction

• aka synthesis reaction

• 2/more reactants combine/merge to make a single product

• A+B→AB

• ex: 2Na(s)+Cl₂(g)→2NaCl(s)

2Na(s)+Cl₂(g)→2NaCl(s)

solid sodium reacts with chlorine gas to form solid sodium chloride

decomposition reaction

• single compound breaks down into 2/more simpler products

• AB→A+B

• 2H₂O(l)→2H₂(g)+O₂(g)

2H₂O(l)→2H₂(g)+O₂(g)

liquid water breaks down to form hydrogen gas and oxygen gas

single displacement reaction

• 1 reactant replaces part of the other reactant compound to produce 2 new compounds

• similar(type: metal or non OR # of ve^-) elements replace each other

• A+BC→AC+B

• Cl₂(g)+2KBr(aq)→2KCl(aq)+Br₂(l)

Cl₂(g)+2KBr(aq)→2KCl(aq)+Br₂(l)

chlorine gas reacts w/ aqueous potassium bromide to form aqueous potassium chloride and bromine gas

double displacement reaction

• aka metathesis reaction

• positive and negative ions of 2 ionic compounds exchange places to form 2 new compounds

• cation(metal) replaces cation, anion(non) replaces anion

• AB+CD→AD+CB

• A and C - metals, B and D - non

• CaCl₂(aq)+Na₂CO₃(aq)→CaCO₃(s)+2NaCl(aq)

CaCl₂(aq)+Na₂CO₃(aq)→CaCO₃(s)+2NaCl(aq)

Aqueous calcium chloride reacts with aqueous sodium carbonate to form solid calcium carbonate and aqueous sodium chloride

combustion reaction

• a substance (usually a hydrocarbon) reacts w/ o2, producing heat and light and gaseous co2 and water vapor

• burning glucose means burning wood

• hydrocarbon+o2→co2+h2o

• CH₄(g)+2O₂(g)→CO₂(g)+2H₂O(g)

CH₄(g)+2O₂(g)→CO₂(g)+2H₂O(g)

gaseous methane reacts w/ oxygen gas to produce carbon dioxide gas and water vapor

types of chem reax summary

combination - 2R→1P

DECOMPOSITION - 1R→2P

S.D. - 3 TYPES

D.D - 4 TYPES

COMBUSTION - C-H + O₂ → CO₂ + H₂O

hydrocarbons

• molecules predominantly composed of hydrogen and carbon

• aka organic compounds, basis of organic moles and essential to life and industry

• can also have some oxygen

• covalent, carbon central atom

• fuel, always paired w/ o2 in combustion reactions

• can exist as 3 forms

• ex: natural gas, polyethylene, butane

organic

things w/ rich amt of carbon

general physical characteristics of hydrocarbons

1. state of matter (solid, liquid, or gas)

2. density (less than water)

3. Solubility (insoluble w/ water but soluble w/ other HCs and nonpolar/nonreactive solvents)

4. low boiling and melting pts

highly influenced by length and presence of multiple bonds and branches

chemical characteristics of hydrocarbons (3 forms)

1. linear: long chain

2. branched: long chain w/ side chain

3. cyclic: ring-like chain

law of conservation of mass

always followed by chem equations

solid sulfur(S) reacts w/ oxygen gas to form sulfur oxide gas (SO₂)

S(s) + O₂(g) → SO₂(g)

carbon dioxide gas is produced when solid carbon(C) combines w/ oxygen gas

C(s)+O₂(g) → CO₂

unbalanced equation

can be balanced w/ inspection method or algebraic method (hard)

inspection method

uses/manipulates coefficients but not subscripts

inspection method steps

1. write unbalanced equation

2. count all of involved elements

3. balance

4. check

5. simplify

balancing priorities

1. elements that appear once

2. polyatomic ions

3. all remaining diatomic then monatomic ones

4. hydrogen and oxygen

aliphatic hydrocarbons

• mild/odorless

• linear and branched

• ex: wax and oil

aromatic hydrocarbons

• distinct odor

• cyclic

• ex: benzene, toluene

plastics

• synthetically made HCs

• 500-1000 yrs to decompose bcs contain long chains of single-bonded HCs that make them non-reactive

Chemical structure (bonds)

• key to reactivity

• saturated and unsaturated

saturated HCs

only have single bonds so less reactive bcs single bonds less reactive than double bonds

unsaturated HCs

• have 1 or more double or triple bonds

• more reactive bcs of double/triple bonds and bcs more electrons=more reaction

unsaturated fats

lesser evil compared to saturated bcs easier to react and break down/digest

Double/triple bonds

weak pts or pts of interaction

types of aliphatic HCs

• alkane

• alkene

• alkyne

alkane

• aka paraffins

• saturated bcs all C-C bonds single

• nonpolar and inactive

• found in natural gases and petroleum

• C_nH_2n+2

• no. of carbon prefix + ane

alkene

• aka olefins

• unsaturated bcs atleast 1 double bond

• less hydrogen and more reactive compared to alkanes

• C_nH_2n

• no. of carbon prefix + ene/ylene

• ethane simplest alkene since no 1C alkenes

alkyne

• aka acetylene

• unsaturated bcs has atleast 1 triple bond of carbon

• less hydrogen and more reactive compared to alkanes and alkenes

• C_nH_2n-2

• no. of carbon prefix + yne

common applications of HCs

• energy source

• plastic production

• fabric production

• solvents

• medical applications

energy source

• methane, ethane, propane, butane

• octane

methane, ethane, propane, butane

natural gas for heating, cooking, and electricity generation

octane

powers internal combustion engines in vehicles

plastic production

• ethene/ethylene

• propene/propylene

ethene/ethylene

base chemicals in producing polyethylene(low and high density ppe), used for plastic bags, food packaging, squeeze bottles, and tubing due to its flexible, durable, high impact resistance, and low density

propene/propylene

base chemicals in producing polypropylene, which is used for food containers, bottle caps, automotive parts, medical devices and textiles due to its high temp tolerance

fabric production

ethene and propene for making fibers like polyester and acrylic for clothing, upholstery, and home textiles

solvents

benzene, toluene, and xylene for paints, varnishes, and industrial cleaning solutions bcs effective in dissolving other substances

medical applications

benzene, toluene, and xylene as starting mats in synthesizing complex organic molecules found in drugs (antibiotics, analgesics, antiseptics)

reactivity

alkynes → alkenes → alkanes

no. of hydrogen

alkanes → alkenes → alkynes