Chemical Reactions & Equations PDF CYQ

# ALAKH Sir ke Farrey. ## CHEMICAL REACTIONS AND EQUATIONS ### CHEMICAL REACTION: A process in which new chemicals are formed. ### CHEMICAL EQUATIONS: A chemical reaction with symbols and formulas. * **H2(g) + O2(g) → 2H2O(l)** * **(Reactant)** * **(product)** * **(aq)** - Soluble...

# ALAKH Sir ke Farrey. ## CHEMICAL REACTIONS AND EQUATIONS ### CHEMICAL REACTION: A process in which new chemicals are formed. ### CHEMICAL EQUATIONS: A chemical reaction with symbols and formulas. * **H2(g) + O2(g) → 2H2O(l)** * **(Reactant)** * **(product)** * **(aq)** - Soluble in water * **(Ppt)** - Insoluble in water * **(s)** - Solid * **(g)** - Gas * **↑** - Gas * **↓** - Solid ### BALANCED CHEMICAL REACTION: * Number of Atoms of each element in the chemical equation should be the same as LHS = RHS. * **LHS** * **RHS** * **A2(g) + B2(g) → 2AB(g)** * Why Balance? * Conservation of mass - Total mass of reactants should be equal to the total mass of products. * **Trick:** * First Balance Metals - Zn, Fe, Na, Al, Mg, Mn, Cu, Ca, Rb, Ba * Second Balance Non-Metals - Cl, Br, S, N, P * Third Balance Oxygen, then H. * **Zn + 2HCl → ZnCl2 + H2** * **2Pb(NO3)2 → 2PbO + 4NO2 + O2** ## TYPES OF CHEMICAL REACTION: ### (A) COMBINATION REACTION Two or more reactants combine to form a single product. * **(i) 2Mg(s) + O2(g) → 2MgO(s)** * (ribbon) * (White powder) * Dazzling white light (very bright light) is emitted. * Heat Evolved - Exothermic Reaction. * **(ii) CaO(s) + H2O(l) → Ca(OH)2(aq)** * (Quick lime) * (Slaked lime) * Quicklime reacts vigorously with water. * Rise in temperature (exothermic reaction) * Example of combination and exothermic reaction. * **(vii) C(s) + O2(g) → CO2(g)** * (Burning of coal) ### (B) DECOMPOSITION REACTION One reactants breaks into two or more products. * **(1) Thermal Decomposition** * Thermolysis - breaks due to heat. * **CaCO3(s) + Heat → CaO(s) + CO2(g)** * (limestone) * (Quicklime) * **2FeSO4(s) + Heat → Fe2O3(s) + SO2 + SO3** * (Green) * (Red/Brown) * **4Pb(NO3)2(s) + Heat → PbO(s) + NO2(g) + O2(g)** * (White) * (Yellow) * (Brown gas) * All 3 are thermal decomposition and endothermic reaction. * SO2(g) + SO3(g) are air pollutants. * **(2) Electrolysis Decomposition** * Electrolysis - break due to electric current * **2H2O(l) + Electrolysis → 2H2(g) + O2(g)** * Volume of gas H2:O2 = 2:1. * Pure water is a poor conductor of electricity so a few drops of acids are added which acts as electrolyte and conduct electricity. * **PAO** - Anode oxygen * **(3) Photochemical Decomposition** * Photolysis - Breaks due to light * **2AgCl + sunlight → 2Ag(s) + Cl2(g)** * (White) * (Grey) * **2AgBr + sunlight → 2Ag(s) + Br2(g)** * (Yellow) * (Grey) * Used in black and white photography. ### (C) DISPLACEMENT REACTION * More reactive element replaces a less reactive element from its compound. * **A + BC → AC + B** * **Reactivity series:** * **Potassium (K)** - Most reactive * **Sodium (Na)** * **Calcium (Ca)** * **Magnesium (Mg)** * **Aluminium (Al)** * **Zinc (Zn)** * **Iron (Fe)** * **Lead (Pb)** * **Hydrogen (H)** * **Copper (Cu)** * **Mercury (Hg)** * **Silver (Ag)** * **Gold (Au)** - Less reactive * **Fe(s) + CuSO4(aq) → FeSO4(aq) + Cu(s)** * (Blue) * (Green) * (Red/Brown) * **Zn(s) + CuSO4(aq) → ZnSO4(aq) + Cu(s)** * (Blue) * (Colorless) * (Red) * **Zn(s) + H2SO4(aq) → ZnSO4(aq) + H2(g) + Heat** * H2 gas is colorless and odorless, burns with a pop sound and extinguishes burning candle. * Temperature increases, the reaction is highly exothermic. ### (D) DOUBLE DISPLACEMENT REACTION: * Exchange of ions between reactants. * **AB + CD → AD + BC** * **Na2SO4(aq) + BaCl2(aq) → BaSO4(s) + 2NaCl(aq)** * (Colorless) * (Colorless) * (White ppt) * **Pb(NO3)2 + 2KI(aq) → PbI2(s) + 2KNO3(aq)** * (Colorless) * (Colorless) * (Yellow ppt) * Example of double displacement and precipitation reaction. ## HEAT IN REACTIONS: ### (A) Exothermic Reaction * **A + B → C + Heat** * **(1) Respiration** * **Glucose + O2 → CO2(g) + H2O(l) + Energy** * **(2) Burning of naturalgas** * **CH4(g) + O2(g) → CO2(g) + H2O(g) + Heat** * **(3) Decomposition of vegetables into compost** ### (B) Endothermic Reaction * **A + B + Heat → C** * All examples of decomposition reaction. * **2FeSO4 + Heat → Fe2O3(s) + SO2(g) + SO3(g)** * **CaCO3(s) + Heat → CaO + CO2(g)** ## REDOX REACTION The reaction in which oxidation and reduction occur. ### Oxidation * If a chemical (A)→ **loss of electron** * **Gain of oxygen** * **Loss of hydrogen** * It is called oxidation of 'A' and 'A' is said to be oxidized. * **Cu(s) + O2(g) + Heat → CuO(s)** ### Reduction * If chemical (B) → **Gain of e** * **Loss of O2 (oxygen)** * **Gain of hydrogen** * It is called reduction of 'B' and 'B' is said to be reduced. * **CuO(s) + H2(g) + Heat → Cu(s) + H2O** # ZnO + c ## oxidised (+0) ## (oxidising agent ## (Reducing ## agent) Reduced (-0) ## Zn + co ## CORROSION: When a metal is attacked by substances around it such as moisture (water vapor + oxygen), acid etc., it is said to be corroded and this process is called corrosion. Examples of corrosion: * **Rusting of iron - Hydrated Reddish Brown Iron Oxide (Rust)** * **Tarnishing of copper - Green** * **Tarnishing of silver - Black** ## RANCIDITY: The taste or smell of food material containing fat/oil changes when it is left exposed to air for a long time. * Oxidation of fat/oil present in food material causes rancidity. * **Prevention:** * Antioxidants * Airtight container * Bags of chips (Flushed with N2 gas) ## PHYSICAL CHANGE AND CHEMICAL CHANGE * **No chemical reaction happens** * **No new chemical is formed** * Examples: * Boiling water from the evaporating dish * Melting of ice to give water * Melting of wax * Crushing a paper cup * Crystallization * **A chemical reaction happens** * **Shape, size, colour, etc., may also change** * **Examples:** * Burning of paper * Fermentation of grapes * Souring of milk * Curd from milk is left in a room during summer * Rusting of iron * Food digestion * Food cooking * Chemical Battery usage ## CURRENT YEAR QUESTIONS (CYQ) **Question-1)** To balance the following chemical equation, the values of the coefficients x, y, and z must be respectively. * **xZn(NO3)2 + Heat → yZnO + zNO2 + O2** * (a) 4, 2, 2 * (b) 4, 4, 2 * (c) 2, 2, 4 * (d) 2, 4, 2 * **Balancing a chemical equation or why do you balance a chemical equation?** **Question-2)** Ravi was cleaning up his setup when he found a small box containing old chemicals. Among them was a bottle of ferrous sulphate crystals. Curious about the contents, he decided to heat a small portion of the crystals in a dry container, hoping to see some change As the heat intensified, he observed something unexpected happening to the crystals. * **(a)** List any two observations he will make. * **(b)** What type of chemical reactions is occurring when ferrous sulphate is heated? * **(c)** Write the balanced chemical equation for the reaction and name the product **Question-3)** During a chemistry practical session, Neha and her friends were assigned an experiment. Their teacher provided them with a white crystalline compound in a small test tube and instructed them to heat it gently over a flame using a spirit lamp. As Neha observed, the white compound started decomposing releasing two different gases. One of the gases had a distinct brown colour, which spread across the test tube, while the other was colorless and had no noticeable odor. A solid yellow residue was left behind at the bottom of the test tube after heating. * **(a)** Identify the type of chemical reaction that occurred during the reaction. * **(b)** Write the balanced chemical equation for the reaction. * **(c)** What is the name of the brown gas that evolved during the reaction? * **(d)** Name the yellow residue left in the test tube and suggest a simple method to test whether it is acidic or basic. **Question-4)** A student mixes sodium sulphate powder in barium chloride powder. What change would the student observe on mixing the two powders? Justify your answer and explain how he can obtain the desired change. **Question-5)** In a school lab, a group of students decided to demonstrate the electrolysis of water as part of their chemistry project. They carefully set up the experiment, filling a beaker with water and placing two electrodes into it To ensure the process was efficient, they added a few drops of dilute sulphuric acid to the water. As an electric current passes through the water, they observed the formation of gas bubbles at both electrodes over time. They noticed that one test tube had twice the amount of gas compared to the other. This observation prompted the students to analyze the phenomenon in more detail. Based on this experiment, answer the following questions. * **(a)** Identify the gases produced at the anode and the cathode during the electrolysis of water. * **(b)** Explain why the volume of gas collected at one of the electrodes is twice the volume at the other electrode. * **(c)** What do you think would happen if dilute sulphuric acid was not added to the water before the experiment? **Question-6)** Which of the following is a redox reaction, but not a combination reaction? * **(a) C + O2 → CO2** * **(b) 2H2 + O2 → 2H2O** * **(c) 2Mg + O2 → 2MgO** * **(d) Fe3+ + 3CO → Fe + 3CO2** **OR** In the Redox reaction MnO2 + 4HCl → MnCl2 + 2H2O + Cl2 * **(a)** MnO2 is reduced to MnCl2 and HCl is oxidized to H2O. * **(b)** MnO2 is reduced to MnCl2 and HCl is oxidized to Cl2. * **(c)** MnO2 is oxidized to MnCl2 and HCl is reduced to Cl2. * **(d)** MnO2 is oxidized to MnCl2 and HCl is reduced to H2O. **Question-7)** 2g of silver chloride is taken in a china dish and the china dish is placed in sunlight for sometime What will be your observation in this case? Write the chemical reaction involved in the form of a balanced chemical equation - identify the type of chemical reaction. **Question-8)** Classify the following reactions into different types of reactions. * **(i) AgNO3(aq) + NaCl(aq) → AgCl(s) + NaNO3(aq)** * **(ii) CaO(s) + H2O(l) → Ca(OH)2(aq)** * **(iii) 2KClO3 (s) → 2KCl (aq) + 3O2 (g)** * **(iv) Zn + CuSO4 → ZnSO4 + Cu** **Question-9)** You might have noted that when copper powder is heated in a china dish, the reddish brown surface of copper powder becomes coated with a black substance. * **(a)** Why has this black substance formed? * **(b)** What is the black substance? * **(c)** Write the chemical equation of the reaction that takes place. * **(d)** How can the black coating on the surface be turned reddish brown? **Question-10)** During a science exhibition, Aryan and his friends set up an experiment to demonstrate the properties of metals. They took a shiny piece of metal, 'M' , and held it carefully with tongs over a Bunsen burner. As the metal heated up, it started to burn with a dazzling white flame, catching the attention of everyone around. After the flame died out, they noticed a fine white powder 'N' left on the metal plate beneath the burner The group wondered what had caused the transformation. Their teacher challenged them to explain the process and its scientific basis. * **(a)** Identify the shiny metal 'M' and the white powder 'N' formed during the reaction. * **(b)** Represent the reaction with a balanced chemical equation. * **(c)** Did the shiny metal 'M' undergo oxidation or reduction during the reaction? Support your answer with reasoning. **Question-11)** What happens when food materials containing fats and oils are left for a long time? List two observable changes and suggest three ways by which this phenomenon can be prevented.