6.1 Chemical equations

Question 1

What are chemical equations

Answer 1

Chemical Equations show a chemical reaction which causes chemical changes in the involved substances

Question 2

How can you show chemical equations

Answer 2

It can be written in words: hydrogen plus oxygen produce water

but using chemical formulas is usually better: H2 + O2 → H2O (this formula is unbalanced)

Question 3

explain reactants and products

Answer 3

in a chemical reaction the initial substances are called the reactants, they will experience chemical changes to become the product(s)

Question 4

What are the two types of reaction related to energy

Answer 4

these reactions will either be exothermic (produces energy) or endothermic (consumes energy),

Reactants → Products + Energy, Exothermic

Reactants + Energy → Products, Endothermic

Question 5

What does the + symbol mean

Answer 5

+ means “plus” or “and”

Question 6

What does the -> symbol mean

Answer 6

→ means “yields” or “produces”

Question 7

what does the (s) symbol mean

Answer 7

(s) means the substance is a solid

Question 8

what does the (l) symbol mean

Answer 8

(l) means the substance is a liquid

Question 9

What does the (g) symbol mean

Answer 9

(g) means the substance is a gas

Question 10

what does the (aq) symbol mean

Answer 10

(aq) means the substance is dissolved in water (aqueous)

Question 11

What do subscript numbers mean

Answer 11

subscript numbers indicate the number of the preceding element in the compound

Question 12

What do coefficient numbers mean

Answer 12

coefficient numbers indicates how many of the compound / element are present for the equation to be balanced, either moles or individual compounds, a ratio

Question 13

What does N.R mean

Answer 13

N.R. means No reaction

Question 14

What is balancing an equation

Answer 14

Equations must be balanced so that their isn’t extra or missing atoms at the end

balancing an equation involves ensuring an equal number of each atom is present before and after the reaction.

Ex: H2 + O2 → H2O is unbalanced as 1O is unaccounted for, while 2H2 + O2 → 2H2O is balanced

there should be 4 hydrogen and 2 oxygen atoms before and after the reaction

Question 15

What do the coefficient numbers in a balanced equation indicate

Answer 15

the numbers in a balanced chemical equation, can represent moles of atoms and molecules as well as individual atoms and molecules, depending on scale.

Question 16

What is the law of conservation of mass

Answer 16

TheLaw of Conservation of Massis the rationale for balancing a chemical equation. The law wasdiscovered by Antoine Laurent Lavoisier (1743-94) and this is his formulation of it, translated into English in 1790 from theTraitmentaire de Chimie(which was published in 1789):

“We may lay it down as an incontestable axiom, that, in all the operations of art and nature, nothing is created; an equal quantity of matter exists both before and after the experiment; the quality and quantity of the elements remain precisely the same; and nothing takes place beyond changes and modifications in the combination of these elements.”

A less wordy way to say it might be: “Matter is neither created nor destroyed.”

Question 17

What is the process of balancing an equation

Answer 17

Balancing an equation involves a trial and error method of repeatedly changing the coefficients before compounds until it is balanced

Question 18

In a chemical reaction what is conserved / not conserved

Answer 18

• mass is conserved, and
• atoms are conserved
• molecules are not necessarily conserved
• Total energy is conserved (though harder to determine)