Hon Chem: Combustion Part 2 A
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) ( = 0.897 J/(gi°C))10 g of Ag(s) (= 0.234 J/gi°C )10 g of Fe(s) ( = 0.450 J/gi°C)10 g of Zn(s) ( = 0.387 J/gi°C )From first to last, which lists the order in which these samples will reach 90.0°C? Al, Fe, Zn, Ag Ag, Zn, Fe, Al Al, Fe, Ag, Zn Ag, Al, Zn, Fe
Ag, Zn, Fe, Al
Which statement about exothermic reactions is accurate? As reactants form products, the potential energy decreases. As reactants form products, the potential energy increases. Thermal energy is transferred from the product to the reacting substances. Thermal energy is transferred from the surroundings to the reacting substances.
As reactants form products, the potential energy decreases
An ice cube is placed on a kitchen counter. Which best describes heat flow in this situation? Heat flows from the ice to the counter, causing the molecules in the counter to move more quickly. Heat flows from the ice to the counter, causing the molecules in the counter to move more slowly. Heat flows from the counter to the ice, causing the molecules in the counter to move more quickly. Heat flows from the counter to the ice, causing the molecules in the counter to move more slowly.
Heat flows from the counter to the ice, causing the molecules in the counter to move more slowly
Which statement about Hf is true? It is zero for any compound in its standard state. It is positive when the bonds of the product store more energy than those of the reactants. It is negative when a compound forms from elements in their standard states. It is zero for any element that is in the liquid state.
It is positive when the bonds of the product store more energy than those of the reactants
Which units express specific heat capacity? J/°C, J/K, cal/°C, cal/K J/(gi°C), J/(giK), cal/(gi°C), cal/(giK) J, cal °C, K
J/(gi°C), J/(giK), cal/(gi°C), cal/(giK)
Which units express heat capacity? J/°C, J/K, cal/°C, cal/K J/(gi°C), J/(giK), cal/(gi°C), cal/(giK) J, cal °C, K
J/°C, J/K, cal/°C, cal/K
A generator contains a coil that spins to produce an electric current. How is energy transformed by using a generator? Thermal energy is transformed to potential energy. Thermal energy is transformed to mechanical energy. Chemical energy is transformed to electromagnetic energy. Mechanical energy is transformed to electromagnetic energy.
Mechanical energy is transformed to electromagnetic energy
A student touches a freshly baked cake that was taken out of the oven. Which best explains why the cake feels hot? Molecules in the skin are moving faster than molecules in the cake. Molecules in the cake are moving faster than molecules in the skin. The kinetic energy of molecules in the cake is more than the energy in the baking tray. The kinetic energy of molecules in the baking tray is more than the energy in the cake.
Molecules in the cake are moving faster than molecules in the skin
Which statement is true if the Hrxn of a reaction is positive? The reaction is endothermic. The reaction is exothermic. There is more reactant than product. There is more product than reactant.
The reaction is endothermic
The initial temperature of a bomb calorimeter is 28.50°C. When a chemist carries out a reaction in this calorimeter, its temperature decreases to 27.45°C. If the calorimeter has a mass of 1.400 kg and a specific heat of 3.52 J/(gi°C), how much heat is absorbed by the reaction? Use q=mcp (triangle) T 140 J 418 J 1,470 J 5,170 J
5,170 J
A baker touches a pie right after taking it out of the oven. Which statement best explains why the pie feels hot? Molecules in the skin move faster than molecules in the pie, so heat is transferred to the pie. Molecules in the pie move faster than molecules in the skin, so heat is transferred to the skin. Molecules in the skin move faster than molecules in the pie, so heat is transferred to the skin. Molecules in the pie move faster than molecules in the skin, so heat is transferred to the pie.
Molecules in the pie move faster than molecules in the skin, so heat is transferred to the skin
An arrow is fired at a target on a high wall. How does the energy change between the moment the arrow is fired and the moment it hits the target? The potential energy and kinetic energy remain the same. The potential energy decreases as kinetic energy increases. The kinetic energy decreases as potential energy increases. The kinetic energy remains at zero, but potential energy increases.
The kinetic energy decreases as potential energy increases
Old photographic flashbulbs burn magnesium metal in a reaction that causes a flash of brilliant white light. A photographer would need to take care not to suffer burned fingers when trying to replace the hot bulb. What best identifies the energy transformation that occurs in the flashbulb? chemical energy to electromagnetic energy and thermal energy electromagnetic energy to chemical energy and thermal energy chemical energy to electromagnetic energy thermal energy to chemical energy
chemical energy to electromagnetic energy and thermal energy
In what type of reaction or process does heat flow into the system? combustion exothermic condensation endothermic
endothermic
The enthalpy of formation for C6 H6 (I) is 49.0 kJ/mol. Consider the following reaction.Is the reaction endothermic or exothermic, and what is the enthalpy of reaction? Use Hrxn = (Hf, products) - (Hf, reactants) exothermic; Hrxn = 49.0 kJ exothermic; Hrxn = -49.0 kJ endothermic; Hrxn = 49.0 kJ endothermic; Hrxn = -49.0 kJ
endothermic; Hrxn = 49.0 kJ
A baseball player hits a ball. Which is the best description of the energy of the ball as it flies over the pitcher's head? chemical kinetic nuclear thermal
kinetic
In a chemical reaction occurring in an open beaker, the reactants have a mass of 10.0 g and contain 1000 J of energy. The products in the beaker contain a mass of 5.0 g and 500 J of energy. Which best explains the difference in energy and mass as reactants are converted to products? kinetic energy closed systems law of conservation of energy electromagnetic energy
law of conservation of energy
Consider the following intermediate chemical equations.In the final chemical equation, NaCl and O are the products that are formed through the reaction between and Cl. Before you can add these intermediate chemical equations, you need to alter them by multiplying the second equation by 2. multiplying the first equation by 2. multiplying the first equation by (1/2). multiplying the second equation by (1/4).
multiplying the first equation by 2.
Which is the best term to use when describing the energy of position? chemical kinetic potential electromagnetic
potential
Thermal energy is the energy associated with electric fields. being stored in chemical bonds. the pull of gravity. temperature.
temperature
Which statement defines the heat capacity of a sample? the temperature of a given sample the temperature that a given sample can withstand the quantity of heat that is required to raise the sample's temperature by 1°C (or Kelvin) the quantity of heat that is required to raise 1 g of the sample by 1°C (or Kelvin) at a given pressure
the quantity of heat that is required to raise the sample's temperature by 1°C (or Kelvin)
What is enthalpy? the total concentration of the system the total heat content of the system the total pressure of the system the total disorder of the system
the total heat content of the system
When 40.0 mL of 1.00 M H2SO4 is added to 80.0 mL of 1.00 M NaOH at 20.00°C in a coffee cup calorimeter, the temperature of the aqueous solution increases to 29.20°C. If the mass of the solution is 120.0 g and the specific heat of the calorimeter and solution is 4.184 J/g • °C, how much heat is given off in the reaction? (Ignore the mass of the calorimeter in the calculation.) Use q=mcp (triangle) T 4.62 kJ 10.0 kJ 14.7 kJ 38.5 kJ
4.62 kJ
Which statement is correct about the law of conservation of energy? Energy is created when water freezes. Energy is destroyed when sugar is burned. Energy stays inside molecules permanently. Energy is transferred when atoms are rearranged.
Energy is transferred when atoms are rearranged
Heat that flows by conduction is the transfer of thermal energy between substances in contact. What must occur for this to happen? The two systems must be the same temperature. The two systems must not be touching each another. One system must have higher kinetic energy than the other system. The thermal energy of one system must be the same as the thermal energy of the other system.
One system must have higher kinetic energy than the other system
A hot metal plate at 150°C has been placed in air at room temperature. Which event would most likely take place over the next few minutes? Molecules in both the metal and the surrounding air will start moving at lower speeds. Molecules in both the metal and the surrounding air will start moving at higher speeds. The air molecules that are surrounding the metal will slow down, and the molecules in the metal will speed up. The air molecules that are surrounding the metal will speed up, and the molecules in the metal will slow down.
The air molecules that are surrounding the metal will speed up, and the molecules in the metal will slow down
Which is the best example of potential energy? holding a basketball in the air rolling a ball across a flat table flowing electric current through a wire turning on a flashlight in a dark room
holding a basketball in the air
The heat capacity of a sample should be divided by which quantity to find the specific heat capacity? temperature in degrees Celsius temperature in kelvins volume in liters mass in grams
mass in grams
Ammonia (NH3 (g), Hf = -45.9 kJ/mol ) reacts with oxygen to produce nitrogen and water (H2 O(g), Hf = -241.8 kJ/mol) according to the equation below.What is the enthalpy of the reaction? Use Hrxn = (Hf, products) - (Hf, reactants) -3,572.1 kJ -1,267.2 kJ 1,267.2 kJ 3,572.1 kJ
-1,267.2 kJ
Ethyne (C2 H2 (g), Hf = 226.77 kJ/mol) undergoes complete combustion in the presence of oxygen to produce carbon dioxide (CO2 (g), Hf = -393.5 kJ/mol ) and water (H2 O(g), Hf = -241.82 kJ/mol) according to the equation below. What is the enthalpy of combustion (per mole) of C2 H2 (g)? Use Hrxn = (Hf, products) - (Hf, reactants) -2511.2 kJ/mol -1255.6 kJ/mol -862.1 kJ/mol -431.0 kJ/mol
-1255.6 kJ/mol
Butane (C4 H10(g), Hf = -125.6 kJ/mol) reacts with oxygen to produce carbon dioxide (CO2 , Hf = -393.5 kJ/mol ) and water (H2 O, Hf = -241.82 kJ/mol) according to the equation below.What is the enthalpy of combustion (per mole) of C4H10 (g)? Use Hrxn = (Hf, products) - (Hf, reactants) -2,657.5 kJ/mol -5315.0 kJ/mol -509.7 kJ/mol -254.8 kJ/mol
-2,657.5 kJ/mol
A sample of an unknown substance has a mass of 0.465 kg. If 3,000.0 J of heat is required to heat the substance from 50.0°C to 100.0°C, what is the specific heat of the substance? Use q=mcp (triangle) T 0.00775 J/(gi°C) 0.0600 J/(gi°C) 0.129 J/(gi°C) 0.155 J/(gi°C)
0.129 J/(gi°C)
A sample of hexane (C6H14) has a mass of 0.580 g. The sample is burned in a bomb calorimeter that has a mass of 1.900 kg and a specific heat of 3.21 J/giK. What amount of heat is produced during the combustion of hexane if the temperature of the calorimeter increases by 4.542 K? Use q=mcp (triangle) T 8.46 kJ 16.1 kJ 27.7 kJ 47.8 kJ
27.7 kJ
Which statement describes how a basic coffee cup calorimeter works? It measures the mass of a substance given the specific heat and temperature of water in a cup of known size. It measures the density of a substance given the mass, specific heat, and temperature of water in a cup of known size. It uses the mass and specific heat of water along with a pressure gauge to measure the gain or loss of energy when a substance is added. It uses the mass and specific heat of water along with a thermometer to measure the gain or loss of energy when a substance is added.
It uses the mass and specific heat of water along with a thermometer to measure the gain or loss of energy when a substance is added
What happens to energy when Sally kicks a soccer ball? Kinetic energy is transformed to chemical energy in muscles. Potential energy is transformed to chemical energy in muscles. Kinetic energy is transferred from the leg to the soccer ball. Potential energy is transferred from the leg to the soccer ball.
Kinetic energy is transferred from the leg to the soccer ball
Two samples of carbon come into contact. A heat transfer will occur between sample A and sample B. What must be true for heat to transfer from sample A to sample B? The average kinetic energy of A is greater than that of B. The average kinetic energy of B is greater than that of A. The average kinetic energy of both samples is equal. The average kinetic energy does not determine the direction of heat transfer.
The average kinetic energy of A is greater than that of B
Two different gases are stored in separate closed containers. If both gases have a temperature of 50°C, which statement is true? The thermal energies of gas molecules in the two containers are unrelated. The gas molecules in both containers will absorb heat from the surroundings. The molecules in one gas will transfer energy to the molecules in the other gas. The gas molecules in both containers have the same average kinetic energy.
The gas molecules in both containers have the same average kinetic energy
The temperature of a sample of liquid water changes from 50°C to 30°C. Which statement best explains the change that must happen at the molecular level? The molecules move more quickly and their average kinetic energy increases. The molecules move more slowly and their average kinetic energy decreases. The molecules move more quickly and their average kinetic energy decreases. The molecules move more slowly and their average kinetic energy increases.
The molecules move more slowly and their average kinetic energy decreases
The Hrxn of formation of carbon dioxide is negative. Which statement is true? The reaction is endothermic. The reaction is exothermic. The amount of carbon dioxide is more than the amount of reactants. The amount of carbon dioxide is less than the amount of reactants.
The reaction is exothermic
If a chemical reaction is reversed, what happens to the enthalpy of the reaction? The enthalpy of the reaction becomes zero. The enthalpy of the reaction doubles. The sign of the enthalpy of the reaction reverses. The enthalpy of the reaction is halved.
The sign of the enthalpy of the reaction reverses
How is enthalpy used to predict whether a reaction is endothermic or exothermic? When the enthalpy of the reactants is higher than the enthalpy of the products, the reaction is endothermic. When the enthalpy of the products is higher than the enthalpy of the reactants, the reaction is exothermic. When the enthalpy change of the reaction is positive, the reaction is exothermic. When the enthalpy change of the reaction is positive, the reaction is endothermic.
When the enthalpy change of the reaction is positive, the reaction is endothermic
