Chemical Reactions Notes Flashcards
What happens in physical changes?
Change of state only.
No new substance formed.
Easy to reverse.
What happens in chemical changes?
Result of a chemical reaction.
New substances formed.
Difficult, if not impossible, to reverse.
The arrow in a equation represents
“goes to”
“reacts to produce”
“yields”
What is (aq) aqueous?
Meaning the substance has been dissolved in water to form a solution
substances you start with in a equation are called the:
reactants
After the reaction has occurred in a equation it is called the:
Products
6 signs of a chemical change
- a gas may be released
- a colour change may occur
- An odour is produced (a distinctive smell)
- a temperature change (either hotter or colder)
- light and/or sound may be produced
- a precipitate is formed (seen as cloudiness in the liquid)
What happens in a precipitate?
A precipitate is solid/s that form when two liquids are mixed together.
what does decomposes mean:
One reactant breaks down into two or more products
Define a chemical reaction?
A chemical reaction is the process of existing substances being converted into different and new substances.
What is a change in phase in a chemical reaction?
A phase change is a physical process in which a substance goes from one phase to another. Usually the change occurs when adding or removing heat at a particular temperature, known as the melting point or the boiling point of the substance.
Define a spontaneous reaction
Chemical reactions are spontaneous if they can occur without adding external energy .For example, a bike will passively rust if left outside. It does not require added energy.
Define non-spontaneous
Chemical reactions are non-spontaneous if the reaction requires external energy (heat or light).
For example, to burn toast, you need to heat it.
What is a combustion reaction?
Reactions in which a substance reacts with oxygen and heat is released. (exothermic)
E.g. CH4(g) + O2 (g) 2H2O (g) + CO2(g) + energy
Examples of combustion reactions include:–
burning of petrol in a car engine.
- burning wax in a candle. - burning gas on the stove in the kitchen
What are the differences between a Complete vs. Incomplete Combustion
A complete combustion (when a lot of oxygen is available), the typical reaction is:
hydrocarbon + oxygen→carbon dioxide + water
Incomplete combustionhappens when there is not enoughoxygento createcarbon dioxide.
In these cases, carbon and carbon monoxide are created instead (or as well as CO2).
What is the ‘conservation of mass’?
Atoms are neither created nor destroyed in a chemical reaction, only rearranged.
product def
the compounds produced by a chemical reaction
reactant def
the starting materials in a chemical reaction
What does a co-efficient and a subscript represent in a chemical equation
2NH3
2 = co-efficient 3= subscript
How do you balance combustion reactions (order to balance)
CHOclate rule: Carbon Hydrogen Oxygen
- What values on a pH scale would be considered acidic?
pH of less than 7 (-1 to 6)
pH>7
- Where would the divide be between strong and weak acids?
A pH of around 5.
That is, a pH -1 to 5 is considered a STRONG acid and 5 to 7 is a WEAK acid.
What values on a pH scale would be considered basic?
Values greater than 7
- Where would the divide be between strong and weak bases?
A pH of around 9.
That is, a pH 7 - 9 is considered a WEAK base and a pH of 9 to 14 is a STRONG base.
What value on a pH scale would be considered neutral?
A pH = 7. Only “pure water” has a pH of 7 and is considered neutral.
Purpose of the pH scale?
A scale that shows how acidic or alkaline a solution is.
Acids ph:
Have pH’s below 7 and the lower the pH the more acidic the solution.
Bases/Alkalis ph:
Have pH’s above 7 and the higher the pH the more alkaline the solution.
Neutral solutions:
Are neither acidic or alkaline and have a pH of exactly 7.
Concentrated vs dilute solution
A concentrated solution has more particles per litre than a dilute solution.
Define pH Indicator
A substance that changes colour to show whether a solution is acidic or basic/alkaline.
Universal indicator:
An indicator that changes colour to show the pH of a solution .
How does litmus paper work?
An indicator. Blue litmus paper turns red on adding acid. Red litmus paper turns blue on adding alkali.
- How do we write a word and chemical equation for a simple neutralisation reaction?
Word equation:
acid + base –> salt + water
- What occurs in a neutralisation reaction? How do we spot them?
A neutralization reaction involves and acid and a base. A hydrogen ion is donated by the acid and the base accepts it. We can spot them because the acid and a base react to form water and a salt. NOTE: A salt is another name for an ionic compound, which consists of a metal caution and a non-metal anion.
Water is formed from the combination of H+ ions and OH- ions to generate water, i.e. H+ + OH- –> H2O. As water is the only substance that is neutral on the pH scale, we call is a neutralisation reaction.
What do all reactions require?
energy
What is activation energy?
the minimum amount of energy needed to break a bond
Endothermic and Exothermic?
An exothermic process releases heat, causing the temperature of the immediate surroundings to rise. An endothermic process absorbs heat and cools the surroundings.”
What is combustion reaction?
In a combustion reaction, a substance reacts with oxygen to form carbon dioxide and water. It requires some sort of ignition source (flame or electrical) and a flame is produced. They are exothermic. (O2 + FUEL -> CO2 + H20)
Chemical equation of respiration?
Respiration chemical reaction:
C6H1206 + 6O2 = 6H20 + 6CO2
Glucose + Oxygen = Carbon Dioxide and Water
What do all acids contain?
Hydrogen ions (H+)
What are some common bases?
They include sodium hydroxide, calcium hydroxide, and ammonia.
What is the pH scale range?
-1 (most acidic) to 14 (most basic)
Some example of strong acids?
Sulfuric acid, nitric acid and hyrdochloric
Some examples of weak acids?
Carbonic acid and ethanoic acid.
Example of strong base?
sodium hydroxide
Example of weak base?
Calcium Carbonate
What does a neutralisation reaction involve?
A neutralisation reaction involves an acid plus a base reacting to form a “salt” (metal and non-metal or it has polyatomic ions) plus water.
Example:
acid + base -> salt + water
Some uses of acids?
Car batteries use a strong acid called sulphuric acid.
Acid can also be used in the Digestion, in animals.
Acids can also be used to remove rust from metals
If the reactants is more than the products in a energy profile diagram is it exothermic or endothermic:
It is exothermic
combustion reactions are Exo or endo?
exothermic
If the reactant is less than the products in a energy profile diagram:
It is endothermic
How to find enthalpy change in a energy profile diagram?
Products-reactants
How do you find the activation energy?
EA (Energy activation) -reactants
The left side of the energy profile digram represents:
Energy (KJ)
Properties of acids:
sour taste corrosive (eats away substances) turns litmus red pH < 7 (at 25 °C) E.g. Sulphuric acid (car batteries) Acetic acid CH3COOH (vinegar) Nitric acid Hydrochloric acid
Properties of bases:
bitter taste slippery/soapy to touch can be caustic turns litmus blue pH > 7 (at 25 °C) used in cleaning products (i.e. soaps, floor cleaner, etc). E.g. Sodium Hydroxide Calcium Hydroxide Bases dissolved in water are known as “alkalis”.
What are acids and bases?
An acid is a molecule that is able to lose or donate a hydrogen cation.
A base is a molecule that is able to gain or accept a hydrogen cation.
Measuring pH
There are many different ways that we can determine if something is acidic or basic.
Litmus paper – red for acids, blue for bases
pH meter – measure precise pH values
Indicators – an indicator changes colour in acids and bases and by comparison.
They can show the approximate pH value.
There are different indicators that can be used
Universal indicator (lots of colours)
Bromophenol Blue
Phenolphthalein (pink or clear)
What does a weak acid mean
A weak acid is an acid that only partially ionises (does not give up all of its hydrogen cations) in water. E.g. Citric acid (C6H8O7) Acetic acid (CH3COOH) Carbonic acid (H2CO3)
What is a strong acid
A strong acid is an acid that almost completely ionises (gives up all of its hydrogen ions) in water.
E.g. Hydrochloric acid (HCl)
Nitric acid (HNO3)
Sulfuric acid (H2SO4)
What is a weak base
A weak base is a molecule that does not protonate completely (does not accept all hydrogen ions). E.g. Ammonia (NH3) Sodium bicarbonate (NaHCO3)
what is a strong base
A strong base is a molecule that almost completely deprotonates an acid (accepts all the hydrogen ions).
E.g. Sodium hydroxide (NaOH)
Potassium hydroxide (KOH).
What is a concentrated acid?
Concentrated acid: lots of acid molecules are found in the solution.
What is a dilute acid?
Dilute acid: not many(or few) acid molecules are found in the solution.
salts
non-metal and metal or polyatomic ions
define Antacids:
The stomach produces dilute hydrochloric acid (HCl), which helps break up food during digestion.
Too much of this acid can be a problem.
Some people take an antacid ‘milk of magnesia’, (Mg(OH)2) to relive the pain.
What is acid rain?
Acid rain is any form of precipitation that contains acidic components, such as sulfuric acid (H2SO4) or nitric acid (HNO3). Normal rain has pH of 5.4. Rain is considered to be acidic if the pH is ≤ 5.2.
What pH does normal rain have and what ph does acid rain have?
Normal rain has pH of 5.4. Rain is considered to be acidic if the pH is ≤ 5.2.
How is acid rain made?
Acid rain is formed when the sulfur dioxide (SO2) and nitrogen oxides (NOx) react with water, oxygen and other chemicals in the air.
These chemical are released into the air by fossil-fuel power plants, vehicles and oil refineries.
Effects of acids rain
Acid rain has many ecological effects, especially on aquatic environments.
It makes them more acidic, which results in more substances being absorbed from the soil and is toxic to aquatic animals.
At higher elevations it is also damaging to forests and inhibit them from growing.
It’s not just plants and animals though that are affected. Acid rain can ruin buildings, bridges, roads and statues by stripping away the material and corroding metal that makes up these structures.
Materials like limestone, marble, steel and brass were originally chosen as they were durable, but now they’re dissolving like a sugar cube in water.
- What can you do as an individual, and what can the global community do to make a difference to the environment with respect to the formation or effects of acid rain?
- A great way to reduce acid rain is to produce energy without using fossil fuels. Instead, people can use renewable energy sources, such as solar and wind power. Renewable energy sources help reduce acid rain because they produce much less pollution.
Full description in which humans activity has caused one type of acid rain?
A human activity that has caused a type of acid rain is the exhaust from cars, trucks, and buses as it releases nitrogen oxides and sulfur dioxide into the air. These pollutants cause acid rain.
What are four states when writing chemical equations?
(s) - solid
(l) - liquid
(g) - gas
(aq) - Aqueous
Molecule definition
Atoms bonded together
Elements definition
One type of atom bonded together that can not be broken.
Mixture definition
Different elements and compounds
Compound definition
Two or more different atoms bonded together
Polyatomic ions definition:
OH-1 hydroxide OH NO3-1 nitrate NO3 CO3-2 carbonate CO3 SO4-2 sulfate SO4 PO4-3 phosphate PO4 CH3COO-1 acetate CH3COO NH4+1 ammonium NH4
Polyatomic ions definition:
OH-1 hydroxide OH NO3-1 nitrate NO3 CO3-2 carbonate CO3 SO4-2 sulfate SO4 PO4-3 phosphate PO4 CH3COO-1 acetate CH3COO NH4+1 ammonium NH4
Examples of fuels
Fossil Fuels (non-renewable):
Gas Fuels: Hydrogas gas, ethane, propane, butane
Liquid Fuels: pentane, octane
Solid Fuels: Coal (carbon)
Combustion reactions
Heating Cooking Internal combustion (engine of a car) Aerobic cellular respiration Rocket fuel
Common Acids and Bases
Acids - Hydrochloric (HCl), Sulfuric (H2SO4), Acetic (CH3COOH), Phosphoric (H3PO4), Nitric (HNO3), Hydrofluoric (HF)
Bases - Sodium hydroxide (NAOH), Calcium hydroxide (Ca(OH)2), Potassium hydroxide (KOH), Sodium carbonate (NaHCO3) Ammonium hydroxide (NH4OH)
What does Δ mean -
Δ means “difference” or “change in”
(DH = DHfinal - DHinitial
DH = DHproducts - DHReactants)
What are antacids -
(Milk of Magnesium(Base)) used to relieve pain of too much acid from digestion of food. This is neutralisation.
What do all acid’s contain?
A hydrogen atom
What is required for particles to do in order to have a reaction to occur?
reactant particles must collide, they must collide at the correct orientation (right way) and
must collide with a minimum amount of energy, EA (to break bonds in reactants)
