THIS IS
YOUR BOOK Reading and listening
ch unit
f ea The opening pages o
Speaking
4
We read about and listen to the topic of the unit, learning about key concepts and developments in physics and chemistry.
Chemical reactions: foundations
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of and consumption of the production (in The earliest evidence Zagros mountains vase found in the 5400 BCE. wine is in a ceramic is dated around and Iraq) which what is now Iran its production process, and even more so Traditionally wine, divine. In fact, both and us to the mysterio and has been related had a god of wine later the Romans ely. the Greeks and s and Bacchus, respectiv lly vineyards: Dionysu ed and eventua changed, develop meant These beliefs and curiosity. This the help of logic that wine resulted disappeared with Ages it was thought while in the juice), that in the Middle (grape osition of matter the result of a from the decomp ed that wine was discover was it 19th Century : fermentation. tion, chemical reaction explained fermenta Louis Pasteur first of The French chemist for the production a scientific basis of and thereby provided the transformation l change involves which wine. This chemica carbon dioxide, ethyl alcohol and , sugar (glucose) into (fungi) such as Candida yeasts of activity Saccharomyces occurs due to the ces or the popular Pichia, Zygosaccharomy science that specialises in the study is now a it’s called? cerevisiae. There Do you know what process. l of these chemica of wine? god Greek the 1 Who was on ble for the producti l reaction is responsi 2 What chemica of wine? tion discovered? 3 When was fermenta tion process? what in the fermenta 4 What turns into fermentation? for ble responsi organisms 5 What are the main
an alternative
Writing tells how from an article that a paragraph taken sions that The following is s and the repercus on. attacked the vineyard powdery mildew save the yearly producti es had in order to the use of fungicid
missing verbs. very few In pairs, fill in the over the year with many challenges especially for The weather ________ much wetter year, lightly. It ______ a warmer regions getting off rains _________ with ns for and generous spring the ideal conditio coastal regions, usual. This ________ but ultimately temperatures than work in the vineyard intense and mildew which ________ Finally, drier weather on yield than quality. retreat. this impacted more tures _____ mildew usual higher summer tempera place earlier than took ment vine develop 14 days earlier _______ Every stage of generally up to the _____ of dates stages last and harvest favoured the A few days of rain g the harvest. to a typical year. without disruptin for many regions rain _____ ripening period del Duero where this ______ Ribera s over whether One exception to difficult decision in the harvest and frequent breaks see, to pick or wait. times), bring, provide, compare, is (three Verbs: coincide, cause, require ishfoodwine/ mspain.com/span ww.foodswinesfro in-2020 -wineSource: https://w ture-de tail/spa ew/feat ures/fea global/ whats-n tml the g harvest.h a paragraph explainin problem and write Now, find a similar 123 issue.
SDG. Reflection on and analysis of SDGs, such as gender equality, climate action, reducing inequalities, etc.
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Writing 122
The audios of each unit’s content are available at www.anayaeducacion.es
We speak about the different issues relating to the unit and the UN Sustainable Development Goals.
Speaking a, s of Galicia, Cataloni s year for the vineyard fungus 2020 was a disastrou to a plague of the and Andalusia, due which Castille-La Mancha powdery mildew, responsible for es to save the harvest. Plasmopara viticola, treatment with fungicid generally requires tion for farmers that: prepare a presenta to going they are how You to the issue and that are relevant • Explains the SDGs fighting can help the farmers al treatment for one alternative/natur • Explain at least
We write a variety of different styles and types of text relating to the unit topic, sometimes relating them to the UN Sustainable Development Goals. By practising different styles of writing, we improve our writing skills.
content development Two types of activities: Understand, think, search… Activities to strengthen learning and relate knowledge.
Unit
ä 1.1 Basic concepts In a chemical reaction, we begin with substances called reactants, which are there before the chemical change. Then, new substances appear called products, which are a result of the chemical change. The reactants must be in contact for a chemical change to occur. Physical changes occur during the process too, which make the change visible. You can see some examples below.
Physical evidence of a chemical change
4
ä 1.3 Writing a chemical reaction: the chemical equation We use chemical equations to describe chemical reaction quantitatively. Chemical equations use stoichiometric coefficients to express the relationship between the reactants and products in a chemical reaction and the proportions of their elemental units. Sometimes, they also give information about other factors, such as the state of matter of substances, their temperature or their pressure. Balancing a chemical equation involves choosing the values of the coefficients, in order to make sure that the number of atoms of each element is the same among the reactants as among the products.
Writing and balancing chemical equations
F ocus on English You probably already know the word equation from maths, as well as from chemistry. Have you ever wondered where it comes from? Equation comes from the Latin word aequatio, which means, an equal distribution. It can be used figuratively: ‘If we take Peter out of the equation, we will find a solution to the situation’. In can also be used in a scientific context, meaning the act of making equal or balanced: ‘To him, the equation was simple: time equals money’.
With a classmate, discuss whether you We will use the example of the reaction between ammonia and molecular catalysts agree with theand following phrase by 5 ENERGY IN CHEMICAL oxygen. The products of this reaction are molecular nitrogen and water. Energy diagrams
ä 5.2
REACTIONS
Albert Einstein: ‘One must divide one’s In the energy diagrams shown on the previous page, only the initial time between politics and equations. and final energy states of the chemical reactions are shown. However, an arrow showing the direction of the reaction: But our equations are much more the evolution of the chemical reaction is more complex than this. Not NH3 + O2 8 N2 + H2O important to me, because politics is for all collisions between molecules are effective since some lack the right the present, while our equations are for orientation or sufficient energy. 2 We choose values for the stoichiometric coefficients to make the number 1 We write the formulas of the reactants and products, separating them with
Energy exchange.
Colour change.
State change.
From the information in the illustration, work out which bonds have broken and which have formed in the chemical change.
of atoms of each element the same among the reactants and the for the transition state (the state between reactants and It isamong possible products. To do so:
2.1 First, we adjust the coefficients of the non-elemental substances: stages. This point in the reaction is called the activated complex (see 2 NH3 + O2 8 N2 + 3 H2O figure below).
During a chemical change, mass is conserved, which means that the total mass of the reactants must equal the total mass of the products. This statement is known as the law of conservation of mass.
Atomic theory and conservation of mass The drawing on the left shows the oxidation of nitrogen monoxide to form nitrogen dioxide.
+ 2 NO
+
We can see that the atoms are in a different order, and that mass is conserved throughout the process. O2
2 NO2
At anayaeducacion.es there is a resource about the evidence of chemical 124
eternity’.
ä 1.2 Atomic theory of chemical reactions The appearance of new substances in a chemical reaction is based on a reordering of the reactant atoms. For this to occur, the elemental units of the reactants must collide. These collisions break bonds and form new bonds, making new substances. Since this is a reordering of atoms, the total mass of the substances before and after the chemical reaction does not change, so we can state that:
Working with pictures
res. with pictu Working city a p your ca Develop and n o rvati for obse . n tio interpreta
1 CHEMICAL CHANGES
changes.
Unit
• The state of matter of the reactants and products, since a state change implies an energy change. • The amount of substance in the reaction, so we must note the values of the stoichiometric coefficients used.
Understand, think, search… 2.2 Then, we do the same for the elemental substances. IfRegardless necessary, we of whether a reaction is endothermic or exothermic, every correct the coefficients we chose before. We can use fractions.
For example, the following thermochemical equation tells us that the combustion of one mole of C4H10, liberates 2 877 kJ if the products are CO2 in gas state and liquid water:
2 NH3 + 3/2 O2 8
1 through 1-2-4.this Draw a table, chemical reaction passes energy state. like the
N2 + 3 H2O
one in the example, for the following reaction:
Activation energy. Catalysts
CH4 + 2 O2 8 CO2 + 2 H2O The energy difference between the reactants Which bonds are transition broken and whichis called the and the energy new bonds form? energy. How many bonds activation are broken how many bonds Thisand energy is a new barrier that will only be form? surpassed by reactant molecules with
Note that the stoichiometric coefficient of molecular E is 1, therefore it is not written. nitrogen
Uncatalysed reaction We can also multiply by two the chemical equation so that there are no fractional coefficients: Activation energy without catalyst, 2 NH3 E+a 3/2 O2 8 N2 + 3 H2O Activation energy with catalyst, Ea' 4 3 2 6 Catalysed 3 Finally we check,REACTANTS element by element, that the number of atoms among the reaction reactants is the same as among the products: Elements
Reactants
H atoms
4 NH3 (4 · 3 = 12)
6 H2O (6 · 2 = 12)
Products PRODUCTS
N atoms
4 NH3 (4 · 1 = 4)
2 N2 (2 · 2 = 4)
O atoms
3 O2 (3 · 2 = 6)
6 H2O (6 · 1 = 6)
REACTION PROGRESS
Understand, think, search…
energy to produce effective 2 Explain sufficient what the stoichiometric
3
collisions. coefficients mean in the exercise above. When this energy is very high and the reactants cannot surpass it, we can use Let’s check.These Balance the lower the catalysts. substances followingactivation chemical reactions energy and create a more a) CO2 +favourable H2O 8 H2CO energetic pathway. This helps 3 the reactants into the products. b) NO +convert O 8 NO 2
2
c) Cr2O3 + Al 8 Al2O3 + Cr d) NO2 + H2O 8 HNO3 + NO e) C2H2 + O2 8 CO2 + H2O
ä 5.3 Energy exchange. Heat of reaction
28 If you touch a beaker containing an
Heat or work can cause an energy exchange between a system and its 125 surroundings or between two systems. When a chemical reaction occurs, there is a variation of the energy in the system which reacts.
29
To measure it, we introduce the concept of the energy of reaction, or heat of reaction, also known as enthalpy:
Search for examples of exothermic and endothermic reactions and their everyday uses.
30 What can you say about a chemical reaction if Qr = –287.9 kJ/mol? And if it has the opposite sign?
31
Write around. Does the presence of a catalyst change the value of Qr?
32 Draw
a diagram representing the exchange of energy in both endothermic and exothermic reactions.
4
ä 5.4 Thermochemical equations Thermochemical equations are equations that tell us not only what substances participate in a chemical reaction but also their state of matter and how much energy they have. The value of the heat of reaction in a thermochemical equation depends on:
products) of a chemical reaction to have more energy than either of these
endothermic reaction, what will you feel?
The icons included with some activities indicate the keys to the project.
The problem solved let you learn reasoning processes and problem-solving strategies.
13 C4H10 (g ) + O2 (g ) 8 4 CO2 (g ) + 5 H2O (l ) Qr = –2 877 kJ 2 For combustion reactions, such as the example, the heat of reaction is called the heat of combustion and is related to a mole of fuel. Sometimes, we can find the heat of reaction on its own in a chemical equation. It will be attached to the reactants in an endothermic reaction and to the products in an exothermic reaction.
Research project Once you have studied this unit, you will be ready to continue with the research project, completing activity 4.
En el apartado «Itinerarios Académicos y Profesionales» de tu banco de recursos encontrarás información sobre los grados superiores relacionados con el desarrollo de energías renovables.
Problem solved 7 Calculate the amount of energy liberated when
We calculate the amount of each fuel:
a kilogram of butane reacts and when a kilogram of methane reacts:
Qr (CH4) = –890 kJ/mol; Qr (C4H10) = –2 877 kJ/mol; M (C) = 12 g/mol, M (H) = 1 g/mol. The heats of combustion refer to a mole of fuel. So, we must calculate the amount of each substance by adding the reactants.
nCH4 =
1 000 g = 62.5 mol 16 g/mol
nC4H10 =
1 000 g - 17.2 mol 58 g/mol
Finally, the heat released by the fuel’s combustion:
First, we must know the molar masses, which we will calculate from the molecular formulas:
Qc (CH4) = 62.5 mol $
MCH4 = 12 $ 1 + 1 $ 4 = 16 g/mol MC4H10 = 12 $ 4 + 1 $ 10 = 58 g/mol
Qc (C4H10) = 17.2 mol $
890 kJ - 5.56 $ 104 kJ 1 mol 2 877 kJ - 4.95 $ 104 kJ 1 mol
The heat of reaction, Qr , is the energy exchanged in heat form between a system containing a chemical reaction and its surroundings. The heat of reaction allows us to distinguish an endothermic reaction from an exothermic one. To do so, we define a sign convention: • Endothermic reactions. In this type of reaction, the energy in the system grows. The exchange of energy via heat goes from the surroundings toward the system so the heat of reaction DE is positive. • Exothermic reactions. In this type of reaction, the energy in the system falls. The exchange of energy via heat goes from the system towards its surroundings so the heat of reaction is negative.
Understand, think, search… 33
The heat of reaction in a thermochemical equation is positive and attached to the reactants. Is the reaction endothermic or exothermic?
34 Calculate the energy necessary to form 75 g of nitric oxide in this reaction:
35
Round table. The heat of combustion of benzoic acid is –26.42 kJ/g: a) Is this an endothermic or exothermic reaction? b) How much energy is released as heat during the combustion of 3 mol of benzoic acid (C7H6O2)?
N2 (g) + O2 (g) + 181 kJ 8 2 NO (g)
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KEYS
PROJECT
SDG SDG Commitment Discover the Sustainable Development Goals and be an active part of our commitment to make a more equal and liveable world.
Developing thinking Work on strategies for thinking: reflect on the content you are learning, generate ideas, organise them, debate them, explain them…
Cooperative learning Get involved in your learning and participate in the group’s learning; you will find that cooperating improves performance and harmony in the class.
Emotional education Get to know yourself; identify the situations that bring up complicated emotions and manage them with constructive, self-affirming experiences.
