12 CHEMICAL REACTIONS KEY Ovál: photo-synthesis Ovál: rusting of iron 1. Warm-up: Which of these processes are chemical reactions and which are not? Why? Ovál: sharpening your knife Ovál: breathing Ovál: alcohol ferments yes yes no Ovál: digestion of food yes yes Ovál: thawing of ice Ovál: burning of coal yes no yes Ovál: dew condensing on a leaf Ovál: rotting of bananas no yes no if it is physical change, i.e. change of state of matter 2. What triggers a chemical reaction http://ed.ted.com/lessons/what-triggers-a-chemical-reaction-kareem-jarrah Make sure you understand the phrases below: increase or decrease of energy structure of proteins potential energy randomness, chaos be likely to react shift to instability combustion of hydrogen and oxygen transition from structure to disorder release energy activate a reaction Explain what is: Enthalpy change of energy Entropy randomness Exothermic reaction heat is released Endothermic reaction heat must be added Describe what this picture means from a chemical point of view info from the video 3. Grammar: Verb Patterns https://advice.writing.utoronto.ca/english-language/gerunds/ Some verbs have the structure verb + object + to… tell, ask, want, would like, remind, invite, warn, advise, expect, encourage, enable, allow, cause …etc. My supervisor encouraged me to repeat the experiments. Intensive heating causes water to evaporate. Our competitors did not expect us to win an award. We invite you to attend the ceremony. We will ask her to prepare a handout. They will require us to submit a summary. Complete the sentences with suitable verb with ‘to ‘ or without ‘to’. Check: 2.00 – 2.50 1. Exothermic reactions are more likely to happen than endothermic ones because they require less energy …………to occur………….. . 2. There’s another independent factor that can make reactions …………happen…………………… – entropy. 3. Shift to higher entropy can allow reactions ……………to start/to happen………………………………. . 4. Transition from structure to disorder gets some reactants past the hump and lets them ……start a reaction………………… . Practice: Discuss several things that can cause/ let/ make/ allow some chemical reactions (to) proceed/ run faster. Write three ideas as sentences with the verb + (to) infinitive structure. Examples: Increased pressure makes some reactions proceed faster. Higher concentration allows the reaction to run faster. Crushing the reactants into powder makes more surface for reacting, which lets reactions proceed faster. 4. Complete the gaps and practise reading the equations. decomposes into combine to produce to react with yield 2H[2]O[2 ] O[2] + 2H[2]O Two molecules of hydrogen peroxide go to form one molecule of oxygen gas plus two molecules of water. CH[4] + 2O[2] CO[2] + 2H[2]O Methane and oxygen …… combine to produce…. carbon dioxide and water. 2C + O[2] 2CO Two atoms of carbon plus one molecule of oxygen …… yield…. two molecules of carbon monoxide. C + O[2] CO[2] Carbon reacts with oxygen to form carbon dioxide. 2 NaOH + H[2]SO[4 ] Na[2]SO[4]+ 2 H[2]O It takes 2 molecules of sodium hydroxide … to react with 1 molecule of sulphuric acid to produce 1 molecule of sodium sulphate and 2 molecules of water. H[2]O H^+ + OH^- Water can break down into hydrogen and hydroxide ions, but hydrogen and hydroxide ions can also combine back together to form water. 2H[2]O[2] 2H[2]O + O[2](g) 2 molecules of H[2]O[2] decompose to form 2 molecules of H[2]O plus one molecule of oxygen gas OR: Hydrogen peroxide … decomposes into water and oxygen gas. 5. Types of reactions – suggest the words. 1. A complex molecule breaks down to form simpler ones. D _ _ _ _ _ _ _ _ _ _ _ _ decomposition 2. Reaction between an acid and base which yields a salt and water. N _ _ _ _ _ _ _ _ _ _ _ _ _ neutralization 3. One reactive element is replaced by another element in a compound formula. D I S _ _ _ _ _ _ _ _ _ displacement 4. Molecules of two reactants exchange some atoms or groups of atoms and give two new compounds; rearrangement takes place. C O N _ _ _ _ _ _ _ conversion 5. Two or more reactants combine to form one product. S _ _ _ _ _ _ _ _ synthesis 6. Reaction of a compound or element with oxygen to form an oxide and produce heat. C O M _ _ _ _ _ _ _ combustion 6. Read these equations and identify the type of reaction according to ex.5. A. The burning of naphthalene C[10]H[8] + 12 O[2] ---> 10 CO[2] + 4 H[2]O B. The combination of iron and sulphur 8 Fe + S[8] ---> 8 FeS C. The electrolysis of water 2 H[2]O ---> 2 H[2] + O[2 ] [ ][] D. Magnesium in water Mg + 2 H[2]O ---> Mg(OH)[2] + H[2 ][] E. The formation of an insoluble salt BaCl[2] + H[2]SO[4] ---> 2 HCl + BaSO[4] F. The reaction of hydrobromic acid with sodium hydroxide HBr + NaOH ---> NaBr + H[2]O A combustion, B synthesis, C decomposition, D displacement, E conversion, F neutralization 7. Forming questions Look at the information from the textbook summary and write questions asking about the underlined parts. Examples Chemical equations are used to describe reactions. Why are chemical equations used? Reactants yield products. What yields products? 1. Equations must be balanced to be consistent with the law of conservation of matter. Why must equations be balanced? 2. Formula weights are determined by adding together the atomic weights of the atoms in the formula unit. What are formula weights determined by? 3. One mole of a substance contains 6.02 x 10^23 units of a substance. How many units of a substance does one mole of a substance contain? 4. The coefficients in an equation give the combining ratio of moles. What gives the combining ratio of moles? 5. The coefficients in an equation give the combining ratio of moles. What do the coefficients in an equation give? D.M. Feigl: General, Organic, and Biological Chemistry, Ch.6, p. 183