C3.3 Calculating and explaining energy change

Question 1

Why is calorimetry used?

Answer 1

To compare the amount of energy released by different fuels and food

Question 2

Describe a simple calorimetry

Answer 2

by using different food or fuels to heat water in a glass of metal container

Question 3

What is energy normally measure in?

Answer 3

joules (J)

Question 4

In the equation

Q = mc (triangle) T

What do the letter stand for and what are the units?

Answer 4

Q- energy transferred (J)

m-mass of water (g)

c- specific heat capacity of water (4.2)

triangle T- Temperature change (Degrees Celsius)

Question 5

How can the amount of energy released or absorbed by a chemical reaction in solution be calculated?

Answer 5

from the measured temperature change of the solution when the reagents are mixed in an insulated container

This method can be used for reactions of solids with water or for neutralisation reactions

Question 6

What can simple energy level diagrams be used to show?

Answer 6

the relative energies of reactants and products, the activation energy and overall energy change of a reaction

Question 7

What happens when bonds are formed?

Answer 7

energy is released

Question 8

What must be needed to break bonds?

Answer 8

energy

Question 9

Describe an exothermic reaction

Answer 9

energy is given out to the surroundings as heat

surroundings become hotter

products have less energy than the reactants

Question 10

Describe an endothermic reaction

Answer 10

Energy is taken in from the surroundings

surroundings become cooler

Products have more energy than the reactants

Question 11

In an exothermic reaction, the products have ……….. energy than the reactants

Answer 11

less

Question 12

In an endothermic reaction, the products have………. energy than the reactants

Answer 12

more

Question 13

In an exothermic reaction, why do the products have less energy than the reactants?

Answer 13

As energy is released into the surroundings

Question 14

In an endothermic reaction, why do the products have more energy than the reactants?

Answer 14

As energy is absorbed from the surroundings

Question 15

In an exothermic reaction, the energy released from forming bonds is….

Answer 15

greater than the energy needed to break existing bonds

Question 16

In an endothermic reaction, the energy needed to break existing bonds is….

Answer 16

greater than the energy released from forming new bonds

Question 17

What 2 ways can hydrogen be used?

Answer 17

• can be burned as a fuel in combustion engines

- can be used in fuel cells that produce electricity to power vehicles

Question 18

What is the word equation for burning hydrogen?

Answer 18

hydrogen + oxygen—— water

Question 19

Why can hydrogen be used as a fuel in combustion engines?

Answer 19

As the reaction between hydrogen and oxygen is exothermic, so it releases energy

when hydrogen reacts with oxygen, more energy is released in bond making than used in bond breaking

Question 20

What are some advantages of using hydrogen in the combustion engine of vehicles?

Answer 20

hydrogen reacts with air to form just water so it is very clean

-produces no polluting gasses

Question 21

What are some disadvantages of using hydrogen in the combustion engine of vehicles?

Answer 21

you need a special, expensive engine

need a lot of energy from another source to produce hydrogen

hard to store safely- explosive

Question 22

How can the relative amounts of energy released when substances burn be measured by?

Answer 22

by a simple calorimetry

Question 23

What is a fuel cell?

Answer 23

an electrical cell that’s supplied with a fuel and oxygen and uses energy from the reaction between them to generate electricity

hydrogen can be used in a hydrogen-oxygen fuel cell

Question 24

What are some advantages of fuel cells in cars?

Answer 24

fuel cell vehicles do not produce any pollutants- eg sulfur dioxide

would eventually help countries become less dependent on crude oil

Question 25

What are some disadvantages of using fuel cells in cars?

Answer 25

hydrogen gas takes up more space to store than liquid petrol

very explosive so difficult to store safely

hydrogen fuel is often made from hydrocarbons (fossil fuel) or by electrolysis of water, which uses electricity

Question 26

What does it mean if the energy transferred is negative?

Answer 26

The reaction was exothermic

Question 27

What does it mean if the energy transferred is positive?

Answer 27

The reaction was endothermic

Question 28

On an exothermic level energy diagram, what does the initial rise represent?

Answer 28

the energy needed to break the old bonds

Question 29

On an endothermic energy level diagram, what does the difference in hight between the reactant and products represent ?

Answer 29

The energy taken in during the reaction

Question 30

What is the activation energy?

Answer 30

The minimum energy needed by reacting particles to break their bonds

Question 31

How can you represent the effect of a catalyst on an energy level diagram?

Answer 31

by drawing a lower curve on the diagram- represents a lower activation energy

Question 32

What are some consequences of using fuels?

Answer 32

releases CO2, a green house gas - causes global warming and climate change

crude oil is running out so it is becoming more expensive- economic effects

Question 33

In a calorimetry experiment, suggest how to reduce energy lost

Answer 33

use a lid

insulate the beaker