Bond energy calculations

Question 1

How is the energy changed shown in exothermic reactions?

Answer 1

• Energy is transferred from chemicals to the surroundings.
• Energy changed is shown as a negative.
• Energy has been transferred from chemicals.

Question 2

How is the energy changed shown in endothermic reactions?

Answer 2

• Energy is gained from surroundings
• Energy changed is shown as a positive.
• Energy has been gained.

Question 3

Bond energies:

Answer 3

• Break a chemical bond- requires energy (endothermic).
• Making bonds- releases energy (exothermic).
• Every chemical bond: energy value.
• Tells us the energy required to break that bond.

Question 4

How do we work out bond energies?

Answer 4

• When bonds are broken= (endothermic).
• Add the bond energies with a + also.
• When bonds are made (exothermic).
• Add a negative.
• Place the right under the left and work it out.