1.Your task is to measure the amount of energy evolved during the combustion of
ID: 539904 • Letter: 1
Question
1.Your task is to measure the amount of energy evolved during the combustion of some hydrocarbon. Which of the following would be the ideal technique for this experiment?
bomb manometry
coffee-cup calorimetry
bomb calorimetry
2. If H = -73.54 kJ for a chemical reaction, that reaction _____________.
cannot occur
is exothermic
is endothermic
3. A reaction where the products are lower in energy than the reactants is an example of an _____.
exothermic process
endergonic process
endothermic process
4. A reaction requires a sample to be heated using a water bath near boiling temperature. Which statement below would be accurate?
Boiling water is an endothermic process and to break apart the intermolecular forces that hold together the water molecules requires +40.7 kJ of energy.
Boiling water is an exothermic process and to break apart the intermolecular forces that hold together the water molecules requires +40.7 kJ of energy.
Boiling water is an endothermic process and to break apart the intermolecular forces that hold together the water molecules requires -40.7 kJ of energy.
5. Given the H°f, calculate the H°rxn for the formation of diamond from graphite. H°f (C, graphite) = 0 kJ/mol H°f (C, diamond) = 2 kJ/mol
-2 kJ/mol
+2 kJ/mol
0 kJ/mol
6. A reaction where the products are higher in energy than the reactants is an example of an _____.
endothermic process
exothermic process
exergonic process
7. A _____ is an experimental set-up that can be used to measure the heat of a chemical reaction or a physical change and determine the specific heat capacity of a substance. manometer
thermometer
calorimeter
8. An increase in water temperature is observed when 1.97 g of NaOH is added. The enthalpy change for this reaction is -2.19 kJ. Which of the statements is accurate?
The H°soln for NaOH is +44.5 kJ/mol so this is an endothermic process where energy in the form of heat is absorbed from the surroundings.
The H°soln for NaOH is -44.5 kJ/mol so this is an exothermic process where energy in the form of heat is absorbed from the surroundings.
The H°soln for NaOH is -44.5 kJ/mol so this is an exothermic process where energy in the form of heat is released into the surroundings.
9. If H = -54.74 kJ for a chemical reaction, that reaction _____________.
cannot occur
is exothermic
is endothermic
10. A chemical reaction that gives off energy in the form of heat is considered _____.
endothermic
exothermic
exergonic
11. Calculate the H°rxn for the combustion of methane using the given H°f. H°f, methane(g) = -74.60 kJ/mol;H°f, water(l) = -285.8 kJ/mol H°f, carbon dioxide(g) = -393.5 kJ/mol
890.5 kJ/mol
-1.04 x 10+3 kJ/mol
-890.5 kJ/mol
12. You are asked to design an experiment to measure the enthalpy of a given reaction. The reaction needs to be at atmospheric pressure so which of the following techniques would be ideal for this experiment?
coffee-cup calorimetry
bomb manometry
bomb calorimetry
13. A chemical reaction that absorbs energy in the form of heat is considered _____.
exergonic
endothermic
exothermic
14. 100 mL of a 0.300 M solution of AgNO3 reacts with 100 mL of a 0.300 M solution of HCl in a coffee-cup calorimeter and the temperature rises from 21.80 °C to 23.20 °C. Assuming the density and specific heat of the resulting solution is 1.00 g/mL and 4.18 J/g °C, respectfully, what is the H°rxn?
+39.0 kJ/mol
+1.17 kJ/mol
-39.0 kJ/mol
15. The following can be used to measure the heat of combustion for an unknown sample?
coffee-cup calorimeter
bomb calorimeter
bomb manometer
16. Bomb calorimetry is carried out at _____.
constant-mass
constant-pressure
constant-volume
17. A drop in water temperature is observed when 0.873 g of ammonium nitrate is added. The enthalpy change for this reaction is +0.280 kJ. Which of the statements is accurate? The H°soln for ammonium nitrate is -25.7 kJ/mol so this is an exothermic process where energy in the form of heat is released into the surroundings.
The H°soln for ammonium nitrate is +25.7 kJ/mol so this is an endothermic process where energy in the form of heat is absorbed from the surroundings.
The H°soln for ammonium nitrate is +25.7 kJ/mol so this is an endothermic process where energy in the form of heat is released into the surroundings.
18. Coffee-cup calorimetry is carried out at _____.
constant-pressure
constant-volume
constant-mass
19. An _____ reaction results when the energy released by the formation of products is greater than the energy required to break the bonds in the reactants.
endothermic
exothermic
exergonic
20. An _____ reaction results when the energy required to break bonds in the reactants is greater than the energy released by the formation of products.
exothermic
endothermic
exergonic
Explanation / Answer
1) OPTION C. To measure the energy of combustion of a hydrocarbon, the hydrocarbon is combusted in a controlled environment taking a specified quantity of the hydrocarbon as a gas, combusting it in a sealed, pressure-resistant container, equipped with a thermometer to sense the temperature change due to combustion. The container which is capable of giving reliable, reproducible data while maintaining such controlled conditions is called "bomb calorimeter" with the latter phrase pointing out its use to measure the change in energy (calorie is a unit of energy) at constant mass and volume unlike coffee-cup calorimeter which calculates energy change at constant pressure.
2) OPTION B. In classical thermodynamics, all the energy expelled from a system is expressed by a "minus" sign preceding its magnitude while that absorbed by the system is given a "plus" sign. In the case given, the enthalpy bears a negative sign, implying that the system is releasing energy. In an exothermic reaction, the total energy of the reactants is higher than that of products and so, energy is released during product-formation. Hence, the given reaction is exothermic. Moreover, the free energy and entropy change of a reaction, not its enthalpy change dictates whether it occurs or not.
3) OPTION A. If the energy of the products are lower than that of the reactants, by the formula for enthalpy of a reaction given by ?Hreaction = ?Hproduct - ?Hreactant we can observe that the final energy change will be negative, as the larger quantity, enthalpy of reactants is substracted from the smaller one - the enthalpy of products. Thus, it can be inferred that energy will be released from the reaction, making it an exothermic process.
4) OPTION A. Boiling water is an endothermic process that results in the breaking of the extensive intermolecular hydrogen-bonding present in water. Since the process is endothermic, heat is absorbed by the system to bring about a change, making the enthalpy a positive quantity.
5) OPTION A. The formation of diamond involves the transformation of graphite to diamond, giving the enthalpy change for it as ?Hreaction = ?Hdiamond - ?Hgraphite which on substitution gives ?Hreaction = 0 - 2kJ/mol = -2kJ/mol.
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