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Questions in chemistry

[Done] Check the correct answer. Which of the following bears a diatomic molecule? i. Helium ii. Nitrogen iii. Sulphur iv. Phosphorus Which of the following is a chemical change? i. Melting of ice ii. Breaking a stone iii. Burning coal iv. Boiling of water Which of the following is an exothermic reaction? i. [tex]$CaO + H _2 O \longrightarrow Ca ( OH )_2$[/tex] ii. [tex]$2 KClO _3 \longrightarrow 2 KCl +3 O _2$[/tex] iii. [tex]$N _2+ O _2 \longrightarrow 2 NO$[/tex] When a piece of granulated zinc was added into the test tube containing dilute HCl, a gas was produced. What gas is it? i. Carbon dioxide ii. Ammonia iii. Oxygen iv. Hydrogen What does the symbol ([tex]$\rightleftharpoons$[/tex]) represent? i. Reactant ii. Product iii. Endothermic reaction iv. Reversible reaction What gas will be produced if [tex]$KClO _3$[/tex] is heated? i. Hydrogen ii. Oxygen iii. Chlorine iv. Potassium If limestone is heated, what will be the products? i. [tex]$Ca ( OH )_2+ O _2$[/tex] ii. [tex]$CaO + CO _2$[/tex] iii. [tex]$CaO + O _2$[/tex] iv. [tex]$KCl + O _2$[/tex]

[Done] Which of the following diatomic molecules is joined by a double covalent bond? A. $O _2$ B. $N _2$ C. $Cl _2$ D. $H _2$

[Done] The formation of which product(s) will most likely be observed in a combustion reaction? A. an oxide B. one element and one compound C. an element D. two ionic compounds

[Done] Select the correct answer. A compound has an empirical formula of $C _2 H _5$. What is true about this empirical formula? A. It models the structure of the compound. B. It shows the ratio of elements in the compound. C. It gives the mass of each atom in the compound. D. It indicates the number of atoms in the compound. E. It describes only this one compound.

[Done] What is [tex]$\Delta S$[/tex] in the equation [tex]$\Delta G=\Delta H-T \Delta S$[/tex] ? A. The change in heat content between the products and the reactants B. The change in free energy between the products and the reactants C. The change in enthalpy between products and reactants in a reaction D. The change in entropy between products and reactants in a reaction

[Done] Mole of sodium hydroxide reacts with one. Calculate the concentration of the hydrochloric acid. [tex]NaCl + HCl[/tex] Why did the temperature of the mixture fall after the maximum temperature had been reached?

[Done] What prediction can you make about future levels of carbon dioxide $(CO_2)$ in the atmosphere? | Year | Carbon Dioxide, $CO_2$ (ppm) | |---|---| | 1960 | 317 | | 1970 | 326 | | 1980 | 339 | | 1990 | 354 | | 2000 | 371 | | 2010 | 390 |

[Done] Which of the following is an acid? A. LiOH (Lithium hydroxide) B. NH3 (Ammonia) C. H₂SO₄ (Sulfuric acid) D. KOH (Potassium hydroxide)

[Done] A CSTR of volume 1 L (constant density liquid phase) is operated at steady state and constant temperature. The following irreversible reaction occurs: A → C The feed always contains reactant A at the concentration C_A0 = 1 mol/L. The rate depends only on A, and this dependence is expressible by an nth order rate form. Exit concentrations of un-reacted reactant A were measured in two runs. In each run, steady state was achieved at different volumetric flow rates q listed below. | Run | q (L/min) | C_A (mol/L) | |---|---|---| | Run 1 | q_1 = 0.707 | C_A = 0.5 | | Run 2 | q_2 = 0.112 | C_A = 0.2 | (d) Find the order of reaction rounded off to 1 decimal place. V = \frac{f_A F_{A0}}{-r_A} Run 1: 1 = \frac{(0.5)(1)(0.707)}{k_A(0.5)^n} Run 2: 1 = \frac{(0.5)(1)(0.112)}{k_A(0.2)^n} Equating (1) and (2) and solving for n gives n = 1.498.

[Done] Consider the following statements: Statement I: One atomic mass unit is defined as 1/12 of the mass of one carbon-12 atom. Statement II: Carbon-12 isotope is the most abundant isotope of carbon and has been chosen as standard. In the light of the above statements, choose the most appropriate answer from the options given below: A. Statement I is correct but Statement II is incorrect. B. Statement I is incorrect but Statement II is correct. C. Both Statement I and Statement II are correct. D. Both Statement I and Statement II are incorrect.