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