Lesson 4: Half equations

Question 1

What do half equations show?

Answer 1

• Half equations show the gain/ loss of electrons for each element involved in a reaction.

Question 2

What has calcium changed into in this reaction:
Ca + Fe²⁺–> Ca²⁺+ Fe

Answer 2

From Ca –> Ca²⁺

Question 3

What has happened, in terms of electrons, for Ca to turn into Ca²⁺?

Answer 3

• It has lost 2 electrons.

Question 4

What is the half equation for Ca —> Ca ²⁺?

Answer 4

Ca –> Ca²⁺ +2e⁻

Question 5

Where does the electron symbol appear when electrons are lost?

Answer 5

• On the right hand side of the equation.

Question 6

What has iron changed into in this reaction:
Ca + Fe²⁺–> Ca²⁺+ Fe

Answer 6

-Fe²⁺ –> Fe

Question 7

What has happened, in terms of electrons, for Fe²⁺ to turn into Fe?

Answer 7

• It has gained 2 electrons.

Question 8

What is the half equation for Fe²⁺ to Fe?

Answer 8

• Fe²⁺ +2e⁻—> Fe

Question 9

What is the rule for positive ions to form their neutral atoms?

Answer 9

• Positive ions must gain electrons to form their neutral atoms.
  Opposite of what they did to become ion

Question 10

What is the rule for negative ions to form their neutral atoms?

Answer 10

• Negative ions must lose electrons to form neutral ions.
• Opposite of what they did to become ion*

Question 11

What are the 2 TopTips when writing half equations?

Answer 11

1.) Balance atoms/ charge
2.) Remember what existis as molecules.

Question 12

What is the half equation for making water from oxygen?

Answer 12

O₂+4H⁺+4e⁻–> 2H₂O