Topic 5 Energy Changes

Question 1

What is an exothermic reaction?

Answer 1

Transfers energy to surroundings so temperature of surroundings increases

Question 2

What are 3 examples of exothermic reactions?

Answer 2

Combustion
Neutralisation
Many oxidation reactions

Question 3

What are 2 everyday uses of exothermic reactions?

Answer 3

Hand warmers
Self-heating cans

Question 4

What is an endothermic reaction?

Answer 4

Takes in energy from surroundings so temperature of surroundings decreases

Question 5

What are 2 examples of endothermic reactions?

Answer 5

Thermal decomposition
Reaction of citric acid and sodium hydrogencarbonate

Question 6

What is an everyday use of an endothermic reaction?

Answer 6

Sports injury packs

Question 7

What do reaction profiles show?

Answer 7

Relative energies of reactants and products, activation energy and overall energy change

Question 8

What is the activation energy?

Answer 8

Minimum amount of energy that particles must have to react

Question 9

When can chemical reactions only occur?

Answer 9

Reacting particles collide with each other with sufficient energy

Question 10

How is an exothermic reaction represented on a reaction profile?

Answer 10

Products at lower energy level than reactants

Question 11

How are endothermic reactions represented on a reaction profile?

Answer 11

Products at higher energy level than reactants

Question 12

What does the initial rise in energy on a reaction profile represent?

Answer 12

Activation energy

Question 13

What happens during a chemical reaction?

Answer 13

Old bonds broken and new bonds formed

Question 14

What is needed to break bonds in the reactants?

Answer 14

Energy must be supplied

Question 15

What type of process is bond breaking?

Answer 15

Endothermic

Question 16

What happens when new bonds in the products are formed?

Answer 16

Energy released

Question 17

What type of process is bond formation?

Answer 17

Exothermic

Question 18

In an exothermic reaction, what is the energy released from forming new bonds greater than?

Answer 18

Energy needed to break existing bonds

Question 19

In an endothermic reaction, what is the energy needed to break bonds greater than?

Answer 19

Energy released from forming new bonds

Question 20

What can be calculated from bond energies?

Answer 20

Energy needed to break bonds and energy released when bonds are formed

Question 21

How can you calculate the overall energy change in a reaction?

Answer 21

Sum of energy needed to break bonds in reactants minus sum of energy released when new bonds formed in products

Question 22

How can a simple cell be made?

Answer 22

Connecting 2 different metals/electrodes in contact with electrolyte

Question 23

How is a cell set up?

Answer 23

Electrodes connected by wire, voltmeter connected

Question 24

What 2 things is the voltage produced by a cell dependent on?

Answer 24

Electrolyte
Type of electrode

Question 25

What does the **electrolyte** in a **cell contain** that **reacts with the electrodes**?

Answer 25

**Ions**

Question 26

What **causes** the **pd** of a **cell**?

Answer 26

**Different metals react differently** with **same electrolyte**

Question 27

What is the **rule** for **pd** of a **cell**?

Answer 27

**Bigger difference** in **reactivity** of **electrodes, bigger voltage** of **cell**

Question 28

What is a **battery**?

Answer 28

**Two or more cells connected** in **series**, provide **greater voltage**

Question 29

Why does a **battery** have a **greater voltage**?

Answer 29

**Voltages of cells combined**

Question 30

What is an **example** of **non-rechargeable batteries**?

Answer 30

**Alkaline Batteries**

Question 31

When does **electricity stop being produced** in **non-rechargeable cells/batteries**?

Answer 31

**Reactants used up**

Question 32

Why can **rechargeable cells/batteries** be **recharged**?

Answer 32

**Reaction** can be **reversed** by connecting an **external electric current**

Question 33

What are **2 types** of **electrical energy vehicles can use**?

Answer 33

**Batteries** **Hydrogen-oxygen fuel cells**

Question 34

What are **2 disadvantages** of **using batteries (compared to using fuel cells)**?

Answer 34

**Rechargeable batteries** eventually need **replacing** **Batteries store less energy** than **fuel cells**- need **recharging more often**

Question 35

What are **2 disadvantages** of using **hydrogen fuel cells (compared to batteries)**?

Answer 35

**Hydrogen** is **explosive** (when **mixed with air**), **hard to store safely** **Hydrogen** is **gas**- takes up **more space** to **store**

Question 36

What is a **fuel cell supplied with**?

Answer 36

**Fuel** and **oxygen/air**

Question 37

How is a **pd produced** in a **fuel cell**?

Answer 37

**Fuel oxidised electrochemically** within fuel cell

Question 38

What are **hydrogen fuel cells** a **potential alternative to**?

Answer 38

**Rechargeable batteries/cells**

Question 39

What is the **overall reaction** in a **hydrogen fuel cell**?

Answer 39

**Hydrogen oxidised** to **produce water**