Energy in Chemical Reactions Unit Test 88%
A welding torch produces a flame by burning acetylene fuel in the presence of oxygen. This flame is used to melt a metal. Which energy transformation represents this process?
chemical energy into thermal energy
Butane C4 H10 (g),(mc016-1.jpgHf = -125.7), combusts in the presence of oxygen to form CO2 (g) (mc016-2.jpgHf = -393.5 kJ/mol), and H2 O(g) (mc016-3.jpgHf = -241.82) in the reaction: 2C4H10(g) + 13O2(g) -> 8CO2 + 10H2O(g) What is the enthalpy of combustion, per mole, of butane?
-2,657.4 kJ/mol
Nitrogen dioxide, NO2(g) (mc030-1.jpgHf = 33.84 kJ/mol), is decomposed according to the following reaction: 2NO2(g) -> N2(g) + 2O2(g) What is the enthalpy change when 2.50 mol of nitrogen dioxide decomposes?
13.5 kJ of energy absorbed
Complete combustion of a 0.350 g sample of a compound in a bomb calorimeter releases 14.0 kJ of heat. The bomb calorimeter has a mass of 1.20 kg and a specific heat of 3.55 J/(gi°C). If the initial temperature of the calorimeter is 22.5°C, what is its final temperature?
25.3°C
How does the potential-energy diagram for a reaction indicate whether the reaction is endothermic or exothermic?
An endothermic reaction has reactants that are lower in energy than products because energy is absorbed to form the products.
Ammonia, NH3 (Hf = -46.2 kJ), reacts with oxygen to produce water (Hf = -241.8 kJ) and nitric oxide, NO (Hf = 91.3 kJ), in the following reaction: 4NH3(g) + 5O2(g) -> 6H2O(g) + 4NO(g) What is the enthalpy change for this reaction?
-900.8 kJ
Which reaction is endothermic?
6CO2 + 12H2O + energy -> C6H12O6 + 6O2 + 6H2O
What explains the key difference between a bomb calorimeter and a coffee cup calorimeter?
A bomb calorimeter has a separate chamber to hold substances and can even measure heat gain or loss for reactions that do not occur in water.
Loren has the samples of elements that are listed below at room temperature. He exposes the samples to the same heat source until each sample reaches a temperature of 90.0°C. 10 g of Al(s) (mc003-1.jpg = 0.897 J/(gi°C)) 10 g of Ag(s) (mc003-2.jpg= 0.234 J/gi°C ) 10 g of Fe(s) (mc003-3.jpg = 0.450 J/gi°C) 10 g of Zn(s) (mc003-4.jpg = 0.387 J/gi°C ) From first to last, which lists the order in which these samples will reach 90.0°C?
Ag, Zn, Fe, Al
Which statement is true for most chemical reactions?
An energy change occurs during the breaking and forming of bonds.
Which reaction is exothermic?
CH4 + 2O2 mc016-1.jpg CO2 + 2H2O + 891 kJ
A metal sample is heated and placed into the water in a calorimeter at room temperature. Which statement best describes how the calorimeter can be used to determine the specific heat capacity of the metal sample?
Energy transfers from the metal to the water and calorimeter until they are all at room temperature.
Two metal blocks that have slightly different temperatures are placed next to one another. After five minutes, they both have lower but equal temperatures. According to the law of conservation of energy, what most likely happened?
Energy was transferred from the warmer block to the cooler block.
Which statement about enthalpy is true?
Enthalpy is not a state function because its change depends on the identities of the reactants and products
Which statement best describes the direction of heat flow by conduction between two samples of the same material?
Heat flows from faster molecules to slower molecules when they collide.
Which direction does thermal energy flow in the following diagram?
Heat flows from the hand to the ice cream.
Chemical energy in burning wood is changed into thermal energy. The thermal energy is absorbed by water, which boils to produce steam. The thermal energy is changed into kinetic energy in the moving steam. The kinetic energy is used to turn a turbine, which converts the kinetic energy into electricity. Which sentence best describes this system?
It involves both energy transformation and energy transfer.
Which describes the enthalpy change associated with an endothermic reaction?
It is positive because the enthalpy of the products is greater than the enthalpy of the reactants.
An arrow is fired at a target on a high wall. Which statement correctly describes the change in the energy of the arrow as it moves toward the target?
The kinetic energy decreases as potential energy increases.
Which is the best example of how electromagnetic energy is used in everyday life?
a patient receiving an X-ray in a hospital
How should the baking of a pizza be categorized?
as an endothermic process because the dough absorbs heat
The enthalpy of formation for C6 H6 (I) is 49.0 kJ/mol. Consider the following reaction. 6C(s,graphite) + 3H2(g) -> C6H6(l) Is the reaction endothermic or exothermic, and what is the enthalpy of reaction?
endothermic; mc014-5.jpgHrxn = 49.0 kJ
Which best describes heat?
energy that flows from a hot mug of tea to a cold hand
What would be the greatest difference in using an open ceramic coffee mug rather than an insulated mug with a lid as a calorimeter?
exchange of energy with the surroundings
Which statement defines calorimetry?
the measurement of energy that is given off or absorbed in a physical or chemical process
