Energy Changes In Reactions- Exothermic & Endothermic Reactions

Question 1

what is an exothermic reaction

Answer 1

a reaction that transfers energy from the reacting molecules to the surroundings

Question 2

what happens to the temperature of the surroundings during an exothermic reaction

Answer 2

it will increase - surroundings get hotter

Question 3

what type of reactions are exothermic

Answer 3

• combustion
• oxidation
• neutralisation

Question 4

in an exothermic energy profile do the products have less or more energy than the reactants
why?

Answer 4

less energy - because energy is being transferred from the reaction to the surroundings

Question 5

what does the difference between the energy of the reactants and energy of the products tell us?

Answer 5

the amount of energy that has been released into the atmosphere

Question 6

what are two uses of an exothermic reaction

Answer 6

• hand warmers
• self-heating cans e.g. for food or drink

Question 7

what are endothermic reactions

Answer 7

reactions that take in energy from the surroundings

Question 8

what happens to the temperature of the surroundings within an endothermic reaction

Answer 8

temperature decreases

Question 9

what is an example of a endothermic reaction

Answer 9

thermal decomposition

Question 10

for an endothermic energy profile do the products have more or less energy then the reactants
why?

Answer 10

the products have more energy then the reactants because energy is being taken in

Question 11

what does the difference between the energy of the reactants and energy of the products tell us?

Answer 11

the amount of energy that has been taken in by the reaction

Question 12

in both energy profiles what is a similarity, what is this called

Answer 12

the energy rises to a peak - activation energy

Question 13

what is the activation energy

Answer 13

the minimum amount of energy that the particles must have in order to react

Question 14

how do you represent the activation energy on a energy profile

Answer 14

from the reactants to the peak of the curve

Question 15

when we _____ a chemical bond this requires ______. (endothermic)

Answer 15

when we break a chemical bond this requires energy (endothermic)

Question 16

when we ____ a chemical bond we _______ energy (exothermic)

Answer 16

when we make a chemical bond we release energy (exothermic)

Question 17

to calculate the energy change of a reaction you need two key things, what are they?

Answer 17

the structures of the molecules involved
the energy value for each bond

Question 18

is endothermic positive or negative

Answer 18

positive as it gains the energy

Question 19

is exothermic positive or negative

Answer 19

negative as it looses energy

Question 20

for the required practical - temperature changes what is the independent variable, dependent variable and the control

Answer 20

independent variable - volume of sodium hydroxide solution
dependent variable - maximum temperature reached
control variables - volume of hydrochloric acid and the concentrations of both solutions

Question 21

explain the required practical

Answer 21

1. use a bearing cylinder and measure out 30cm^3 of dilute hydraulic acid
2. transfer the acid into a polystyrene cup
3. stand the polystyrene cup inside a beaker
4. use a thermometer to measure the temperature of the acid - record this in a table
5. measure 5^cm3 of sodium hydroxide solution using a measuring cylinder, transfer to polystyrene cup
6. add a lid to the cup and place thermometer through a hole in lid
7. gently stir solution using thermometer
8. this is an exothermic reaction meaning the temperature should go up
9. record the highest temperature reached
10. rinse and dry polystyrene cup
11. carry out the experiment multiple time increasing the amount of sodium hydroxide used by 5cm^3
12. calculate a mean for each volume
13. plot a graph

Question 22

why is a polystyrene cup used

Answer 22

polystyrene is a good thermal insulator helping us to not lose heat