SEM 2 Chemical reactions Exam revision Flashcards
What is a subscript?
Subscripts tell you how many of the atoms are bonded in the compound. The subscript only applies to the element written just before it.
What is a co-efficient?
A co-efficient is a number in front of a chemical formula, that acts as a multiplier. Everything after that co-efficient is multiplied by the co-efficient.
Explain chemical formulas with parenthesis.
The subscript outside the parenthesis, tells you to multiply the elements in the parenthesis
what are the signs of a chemical reaction?
There are six signs that a chemical reaction may have occurred:–
a gas may be released;
a colour change may occur;
An odour is produced;
A temperature change may occur (either hotter or colder);
Light and/or sound may be produced; and,
A precipitate (often seen as cloudiness) may be formed (a precipitate is a solids that forms when two liquids are mixed).
Law of conservation of mass
“Law of conservation of mass” states that matter can be created nor destroyed in a chemical reaction only rearranged. The mass of the reactants equals the mass of the products.
why do we balance chemical equations?
When we write a chemical equation for a reaction, we need to balance the number of atoms on the reactant and product sides to ensure the conservation of mass.
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
complete combustion def
In complete combustion (when a lot of oxygen is available), the typical reaction is:
hydrocarbon + oxygen→carbon dioxide + water
incomplete combustion reaction
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 an acid?
Have pH’s below 7 and the lower the pH the more acidic the solution. An acid is a molecule that is able to lose or donate a hydrogen cation.
What is a base?
Have pH’s above 7 and the higher the pH the more alkaline the solution.A base is a molecule that is able to gain or accept a hydrogen cation.Have pH’s above 7 and the higher the pH the more alkaline the solution.
what is the Ph scale?
The “pH scale” is used to describe how acidic or basic a substance is.
The pH represents the concentration of H+ ions in the solution.
pH = 7: neutral (e.g. pure water – neither acid nor base)
pH < 7: acid (the lower the pH, the stronger the acid)
pH > 7: basic (or alkaline) (the higher the pH, the stronger the base)
What are 3 different ways to measure the 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
weak base vs a strong base
A weak base is when Only a few hydrogen ions are accepted by the base molecules. eg. ammonia NH3
A strong base is where Almost all hydrogen ions accepted by the base molecules. eg Sodium hydroxide NaOH, potassium hydroxide KOH.
What is a neutralization reaction?
Neutralization is a chemical reaction between an acid and a base.
It is another type of double displacement (or double replacement) reaction.
This reaction produces water and a “salt” (or metal salt), which is an ionic compound.
