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Home Question Bank Chemistry Archive 2025 January 05

Chemistry Questions from Jan 05,2025

Browse the Chemistry Q&A Archive for Jan 05,2025, featuring a collection of homework questions and answers from this day. Find detailed solutions to enhance your understanding.

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Soit la réaction chimique suivante 1. Calculer les grandeurs thermo a- la variation de l'enthalpie b-la variation de l'entropie \( \Delta \) c- la variation de l'enthalpie l 2. Etude de l'influence de la temp a- Calculer la'valeur de \( \Delta \mathbf{H}_{r}^{\circ} \). b- Montrer que la variation l'expression : \( \Delta S_{r}{ }^{\circ}(\mathrm{T})=- \) Question 6 Balancing Chemical Equations Balance the following equations showing all workings. (Please note that the symbols in these eactions have been fabricated - they are fictional elements, but you can balance them as formal): ( 2 marks each) I. \( R_{4} V_{10}+\quad L_{2} V \rightarrow L_{3} R V_{4} \) Un gas tiene un volumen de \( 2,5 \mathrm{~L} \) a \( 25^{\circ} \mathrm{C} \). ¿Cuál será su iuevo volumen si bajamos la temperatura a \( 10^{\circ} \mathrm{C} \) ? The first step in the reaction of Alka-Seltzer with stomach acid consists of one mole of sodium bicarbonate \( \left(\mathrm{NaHCO}_{3}\right) \) reacting with one mole of hydrochloric acid \( (\mathrm{HCl}) \) to produce one mole of carbonic acid \( \left(\mathrm{H}_{2} \mathrm{CO}_{3}\right) \), and one mole of sodium chloride \( (\mathrm{NaCl}) \). moles of carbonic acid : \( \sum_{\text {N }}^{\mathrm{N}} \) and 7 mol HCl . Using this chemical stoichiometry, determine the number of moles of carbonic acid that can be produced from \( 4 \mathrm{~mol} \mathrm{NaHCO}_{3} \) mol Esercizio 5. Una sostanza radioattiva, il cesio- \( 137\left({ }^{137} \mathrm{Cs}\right) \) viene analizzato in un laboratorio di ricerca. Dopo quattro giorni si osserva che la massa di questa sostanza si è ridotta del \( 30 \% \) della sua massa iniziale. Determinare il tempo di dimezzamento della sostanza. Se la sostanza viene lasciata decadere per 12 giorni, quale percentuale della sua massa rimarrà? \( [2,3 ; 2,7 \%] \) When a 0.235 g sample of benzoic acid, \( \mathrm{C}_{7} \mathrm{H}_{6} \mathrm{O}_{2} \), is combusted in a bomb calorimeter, a \( 3.62{ }^{\circ} \mathrm{C} \) rise in temperature occurs. When a 0.305 g sample of citric acid, \( \mathrm{C}_{6} \mathrm{H}_{8} \mathrm{O}_{7} \), is burned, a \( 1.83^{\circ} \mathrm{C} \) temperature rise is observed. If the heat of combustion of benzoic acid is \( 26.38 \mathrm{~kJ} \mathrm{~g}^{-1} \), what is the heat of combustion of citric acid? When 1.38 g of liquid \( \mathrm{PCl}_{3} \) at \( 25.55{ }^{\circ} \mathrm{C} \) is added to \( 1.00 \times 10^{2} \mathrm{~g} \) of water at \( 25.55^{\circ} \mathrm{C} \) in a 'coffee-cup' calorimeter, the temperature of the resulting solution increases to \( 32.00{ }^{\circ} \mathrm{C} \). If the specific heat capacity of the solution is \( 4.184 \mathrm{~J}^{\circ} \mathrm{C}^{-1} \mathrm{~g}^{-1} \), and the heat capacity of the Styrofoam cup is negligible, calculate the heat of solution of \( \mathrm{PCl}_{3} \) in water. A 'coffee-cup' calorimeter contains 150 g of water at \( 24.6^{\circ} \mathrm{C} \). A 110 g block of molybdenum metal is heated to \( 100^{\circ} \mathrm{C} \) and then placed in the water in the calorimeter. The contents of the calorimeter come to an average temperature of \( 28.0^{\circ} \mathrm{C} \). What is the specific heat capacity of the molybdenum metal if the specific heat capacity of water is assumed to be \( 4.184 \mathrm{~J}^{\circ} \mathrm{C}^{-1} \mathrm{~g}^{-1} \) ? 3 Bromine is a brown liquid that evaporates easily at room temperature. When a container of bromine is opened, brown gas comes out of the container. Explain why the colour of the brown gas becomes less intense as it gets further away from the container. A 28.2 g sample of nickel is heated to \( 99.8^{\circ} \mathrm{C} \) and placed in a coffee cup calorimeter containing 150.0 g of water at a temperature of \( 23.5^{\circ} \mathrm{C} \). After the metal cools, the final temperature of metal and water is \( 25.0^{\circ} \mathrm{C} \). Calculate the heat capacity of nickel, assuming that no heat escapes to the surroundings or is transferred to the calorimeter.
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