2.5 — formulae and equations

Question 1

what is a balanced equation?

Answer 1

an equation that has equal numbers of atoms for each element on both sides of the equation

Question 2

what are the steps to balancing an equation?

Answer 2

1. write out the unbalanced equation
2. count the number of atoms of each element on both sides
3. add coefficients before formulae to balance atom numbers
4. check if atom numbers are equal on both sides

Question 3

balanced equations obey the law of conservation of mass. what does this mean?

Answer 3

the same mass is retained before and after a reaction

Question 4

where are state symbols written?

Answer 4

after chemical formulae of names of substances in chemical equations

Question 5

what do state symbols indicate?

Answer 5

the physical state of each reactant and product

Question 6

what are the four state symbols?

Answer 6

1. (s) — solid
2. (l) — liquid
3. (g) — gas
4. (aq) — aqueous (dissolved in water)

Question 7

in what reactions can an ionic equation be written?

Answer 7

when the reaction is between ions dissolved in aqueous solution

Question 8

what does an ionic equation show?

Answer 8

only the particles directly involved in the reaction

Question 9

what are the steps to writing out an ionic equation?

Answer 9

1. write out the full balanced equation
2. split soluble ionic compounds into their component ions
3. cancel out any ions that appear unchanged on both sides (spectator ions)
4. check ionic charges balance on both sides

Question 10

what are the ions in an equation that appear unchanged on both sides?

Answer 10

spectator ions

Question 11

what do balanced equations show between reactants and products?

Answer 11

molar ratios

Question 12

in a balanced equation, by rearranging ratios and using molar masses, what can be calculated? (2)

Answer 12

1. mass of product from given mass of reactant
2. mass of reactant needed to produce a given mass of product

Question 13

what are the steps to calculate reacting masses from balanced equations?

Answer 13

1. write out the balanced equation
2. convert given mass into moles
3. use the mole ratio from the equation to calculate moles of the desired species
4. convert moles of the desired into mass