Energy Change

Question 1

endothermic

Answer 1

endo
1. heat energy absorbed, surroundings
2. temp, surroundings fall
3. energy change positive
4. break bonds

exo -> release energy to surrounding
endo -> absorb energy from surrounding

Question 2

all chemical reactions involve…

Answer 2

energy change, surroundings

Question 3

example exothermic reaction

Answer 3

in heat packs
MgO + Acid

Question 4

exothermic

Answer 4

exo
1. heat energy given out, surroundings
2. temp, surroundings rise
3. energy change negative
4. form bonds

Question 5

general types of exothermic reactions

Answer 5

1. combustion, fuel (i.e. burn charcoal)
2. rust iron, corrode metal
3. respiration
4. acid + alkali/carbonate/metal

all reactions mentioned above = form bond energy > break bond energy

exothermic -> heat released to surrounding

Question 6

endothermic reaction e.g.

Answer 6

dissolve ammonium salt
photosynthesis
film photography
thermal decomp.

Question 7

energy lvl, profile diagram
H2o
used for wat?

Answer 7

for any (aq) soln. reaction i.e. aq sodium hydroxide

-572kJ/mol

page 19 https://docs.google.com/document/d/1Ep_FO9CxYSFbxmf3Zqg9mgm9NNyt2enpfMDr49gufrU/edit?tab=t.0

Question 8

reversible reaction

exothermic or endothermic?

Answer 8

forward: exothermic
backward: endothermic

Question 9

define Triangle H

Answer 9

change in energy, reaction

Question 10

how to find out reaction endo/exo w/ energy

Answer 10

energy taken in by reactants - energy released by reactants

WRITE UNITS

depends, break/make bonds, need more energy?
i.e. 25kJ energy break O2 bond, 20 kJ energy bond O and N

1. (break o2 bonds form O, O) 25kJ

minus

2. (form O, N bonds for NO) 20kJ

= +5kJ

Question 11

why req activation energy?

Answer 11

• must absorb energy, need break bond, reaction 2 start

Question 12

similarity between exo, endothermic reactions

Answer 12

Activation energy is the same

Question 13

when triangle H = 0, can reaction?

Answer 13

no
1. reaction did not occur
2. when delta H = 0Kj/mol, break and form same bonds

ALWAYS WRITE UNITS

Question 14

during exothermic reaction

when temp. peaks then drops what does it mean

Answer 14

https://docs.google.com/document/d/1Ep_FO9CxYSFbxmf3Zqg9mgm9NNyt2enpfMDr49gufrU/edit?tab=t.0

page 20

Question 15

for energy change
writing abt breaking, form bond

Answer 15

specify bond
i.e. N-H

Question 16

when triangle H is exothermic….

Answer 16

net heat energy released -> surrounding

Question 17

If a substance is Mr 2, what can be said abt mass?

Answer 17

every 1 mol
2g of substance

Question 18

octane adv, disadv
compared to hydrogen

Answer 18

octane
a: liquid at rtp, easily transport, stored
d: less efficient, release less energy per unit mass (check qn context)