Study "CHEM FINAL", a flashcard deck on FORKSAI.
A gas occupies a volume of 2.50 L at 1.00 atm and 298 K. If the pressure is increased to 3.00 atm and the temperature is raised to 350 K, what will be the new volume of the gas? Show your step-by-step working.
First, use the combined gas law: (P1V1)/T1 = (P2V2)/T2. Given P1 = 1.00 atm, V1 = 2.50 L, T1 = 298 K, P2 = 3.00 atm, T2 = 350 K. Rearranging for V2: V2 = (P1V1T2) / (P2T1). Plugging in the values: V2 = (1.00 atm * 2.50 L * 350 K) / (3.00 atm * 298 K) = 0.98 L. The new volume of the gas will be 0.98 L.
Explain the fundamental difference between a strong electrolyte, a weak electrolyte, and a nonelectrolyte in terms of their dissociation in an aqueous solution.
A strong electrolyte completely dissociates into ions when dissolved in water, leading to high electrical conductivity. A weak electrolyte only partially dissociates into ions, resulting in lower electrical conductivity compared to strong electrolytes. A nonelectrolyte does not dissociate into ions at all when dissolved in water, meaning it does not conduct electricity.
A reaction consumes 15.0 g of hydrogen gas (H2) and 120.0 g of oxygen gas (O2) to produce water (H2O). Which reactant is the limiting reactant? What is the theoretical yield of water in grams? (Atomic masses: H = 1.008 g/mol, O = 16.00 g/mol)
First, write the balanced equation: 2H2(g) + O2(g) -> 2H2O(l). Calculate moles of reactants: Moles H2 = 15.0 g / (2 * 1.008 g/mol) = 7.44 mol. Moles O2 = 120.0 g / (2 * 16.00 g/mol) = 3.75 mol. From stoichiometry, 2 moles of H2 react with 1 mole of O2. For 3.75 mol O2, 2 * 3.75 = 7.50 mol H2 are needed. Since only 7.44 mol H2 are available, hydrogen is the limiting reactant. The theoretical yield of water is calculated from the limiting reactant: 7.44 mol H2 * (2 mol H2O / 2 mol H2) * (18.016 g H2O / 1 mol H2O) = 134 g H2O.
Define the term 'enthalpy of reaction (ΔHrxn)' and explain how its sign (positive or negative) relates to whether a reaction is endothermic or exothermic.
Enthalpy of reaction (ΔHrxn) is the heat change that occurs during a chemical reaction at constant pressure. A negative ΔHrxn indicates an exothermic reaction, meaning heat is released from the system to the surroundings. A positive ΔHrxn signifies an endothermic reaction, where heat is absorbed by the system from the surroundings.
Which of the following statements accurately describes Dalton's atomic theory with respect to modern atomic theory? A) Atoms are indivisible and indestructible. B) All atoms of a given element are identical in mass and properties. C) Atoms of one element can be converted into atoms of another element in chemical reactions. D) Compounds are formed when atoms of different elements combine in simple whole-number ratios.
D) Compounds are formed when atoms of different elements combine in simple whole-number ratios. While Dalton's theory had limitations (e.g., isotopes show atoms of an element can have different masses, and atoms are divisible), the postulate regarding definite composition in compounds remains fundamentally correct and consistent with modern atomic theory.
A student measures the mass of a substance three times, obtaining 10.2 g, 10.3 g, and 10.1 g. The known true value for the mass is 12.5 g. Evaluate the precision and accuracy of these measurements, explaining the roles of systematic and random error.
The measurements (10.2 g, 10.3 g, 10.1 g) are precise because they are close to each other, indicating low random error. However, they are not accurate because they are significantly different from the true value of 12.5 g. This suggests the presence of a systematic error, which consistently causes the measurements to deviate in the same direction from the true value, rather than random fluctuations.
How does the kinetic-molecular theory explain the origin of pressure in a gas and the relationship between temperature and molecular speed?
The kinetic-molecular theory explains that gas pressure arises from the constant collisions of gas particles with the walls of their container. Each collision exerts a force, and the sum of these forces over the area of the walls constitutes the pressure. Furthermore, the average kinetic energy of gas particles is directly proportional to the absolute temperature, meaning as temperature increases, the average molecular speed and the frequency/force of collisions also increase, leading to higher pressure.
Calculate the molarity of a solution prepared by dissolving 25.0 g of potassium hydroxide (KOH) in enough water to make 750.0 mL of solution. (Atomic masses: K = 39.10 g/mol, O = 16.00 g/mol, H = 1.008 g/mol)
First, calculate the molar mass of KOH: 39.10 + 16.00 + 1.008 = 56.108 g/mol. Next, convert grams of KOH to moles: 25.0 g / 56.108 g/mol = 0.4455 mol KOH. Convert the volume from mL to L: 750.0 mL = 0.7500 L. Finally, calculate molarity (moles/volume): 0.4455 mol / 0.7500 L = 0.594 M. The molarity of the solution is 0.594 M.
Distinguish between physical changes and chemical changes, providing an example of each that illustrates the key difference.
A physical change alters the form or appearance of a substance but does not change its chemical composition; for example, melting ice into liquid water is a physical change as H2O molecules remain intact. A chemical change results in the formation of new substances with different chemical compositions and properties; for instance, burning wood is a chemical change because wood reacts with oxygen to form ash, carbon dioxide, and water, which are entirely new substances.
A sample of an unknown gas has a density of 1.96 g/L at STP. Calculate the molar mass of the gas. (R = 0.08206 L·atm/(mol·K))
At STP, T = 273.15 K and P = 1.00 atm. The ideal gas law can be rearranged to find molar mass (M) using density (d): M = (dRT)/P. Plugging in the values: M = (1.96 g/L * 0.08206 L·atm/(mol·K) * 273.15 K) / 1.00 atm. M = 43.9 g/mol. The molar mass of the unknown gas is 43.9 g/mol.