iron reacts with oxygen in a chemical hand-warmer. how should this reaction be categorized? as an exothermic process because it releases heat as an endothermic process because it releases heat as an exothermic process because it absorbs heat as an endothermic process because it absorbs heat
James
Guys, does anyone know the answer?
get iron reacts with oxygen in a chemical hand-warmer. how should this reaction be categorized? as an exothermic process because it releases heat as an endothermic process because it releases heat as an exothermic process because it absorbs heat as an endothermic process because it absorbs heat from EN Bilgi.
Endothermic vs. exothermic reactions (article)
Thermochemistry
Endothermic vs. exothermic reactions
Google ClassroomFacebookTwitter
Let's see what Sam and Julie are up to in the chemistry lab.
Image titled chemistry lab: experiments are fun.
Excited but a bit confused, Sam and Julie run to their chemistry teacher. Sam asks, “Teacher, why did my flask turn cold after adding the salt to water, while Julie’s flask turned hot?”
The teacher replies: “That’s because you were given two different salts. One of your salts generated an endothermic reaction with water, while the other salt generated an exothermic reaction with water. Let me first reveal the identity of your salts: Salt A is ammonium nitrate (
\text{NH}_4\text{NO}_3
NH 4 NO 3
start text, N, H, end text, start subscript, 4, end subscript, start text, N, O, end text, start subscript, 3, end subscript
) and Salt B is calcium chloride (
\text{Ca}\text{Cl}_2
CaCl 2
start text, C, a, end text, start text, C, l, end text, start subscript, 2, end subscript
)."
Now, Sam and Julie are curious about the difference between an endothermic and an exothermic reaction.
Consider the reaction mixture—salt plus water—as the system and the flask as the surrounding.
In Sam’s case, when ammonium nitrate was dissolved in water, the system absorbed heat from the surrounding, the flask, and thus the flask felt cold. This is an example of an endothermic reaction. In Julie’s case, when calcium chloride was dissolved in water, the system released heat into the surroundings, the flask, and thus the flask felt hot. This is an example of an exothermic reaction.
The reaction going on in Sam’s flask can be represented as:
NH4NO3 (s) + heat ---> NH4+ (aq) + NO3- (aq)
You can see, heat is absorbed during the above reaction, lowering the temperature of the reaction mixture, and thus the reaction flask feels cold.
The reaction going on in Julie’s flask can be represented as:
CaCl2 (s) + 2(H2O) ---> Ca(OH)2 (aq) + 2 HCl (g) + heat
In this case, heat is released during the reaction, elevating the temperature of the reaction mixture, and thus Julie’s reaction flask feels hot.
The teacher’s final comment to Sam and Julie about this experiment is, “When trying to classify a reaction as exothermic or endothermic, watch how the temperature of the surrounding—in this case, the flask—changes. An exothermic process releases heat, causing the temperature of the immediate surroundings to rise. An endothermic process absorbs heat and cools the surroundings.”
Based on the above definition, let's pick a few examples from our daily lives and categorize them as endothermic or exothermic.
Endothermic reactions: Heat is absorbed.
1) Photosynthesis: Plants absorb heat energy from sunlight to convert carbon dioxide and water into glucose and oxygen.
6CO2 + 6 H2O + heat ---> C6H12O6 + 6O2
2) Cooking an egg: Heat energy is absorbed from the pan to cook the egg.
Exothermic reactions: Heat is released.
1) Combustion: The burning of carbon-containing compounds uses oxygen, from air, and produces carbon dioxide, water, and lots of heat. For example, combustion of methane (
\text{CH}_4 CH 4
start text, C, H, end text, start subscript, 4, end subscript
) can be represented as follows:
CH4 + 2(O2) ---> CO2 + 2H2O + heat
2) Rain: Condensation of water vapor into rain releasing energy in the form of heat is an example of an exothermic process.
Why is heat released or absorbed in a chemical reaction?
In any chemical reaction, chemical bonds are either broken or formed. And the rule of thumb is "When chemical bonds are formed, heat is released, and when chemical bonds are broken, heat is absorbed." Molecules inherently want to stay together, so formation of chemical bonds between molecules requires less energy as compared to breaking bonds between molecules, which requires more energy and results in heat being absorbed from the surroundings.
What is enthalpy of a reaction?
Enthalpy of a reaction is defined as the heat energy change (
ΔH ΔH Δ, H
) that takes place when reactants go to products. If heat is absorbed during the reaction,
ΔH ΔH Δ, H
is positive; if heat is released, then
ΔH ΔH Δ, H is negative.
\redD{\text{ΔH value negative --> energy released --> exothermic reaction}}
ΔH value negative –> energy released –> exothermic reaction
start color #e84d39, start text, Δ, H, space, v, a, l, u, e, space, n, e, g, a, t, i, v, e, space, --, >, space, e, n, e, r, g, y, space, r, e, l, e, a, s, e, d, space, --, >, space, e, x, o, t, h, e, r, m, i, c, space, r, e, a, c, t, i, o, n, end text, end color #e84d39
\redD{\text{ΔH value positive --> energy absorbed --> endothermic reaction}}
ΔH value positive –> energy absorbed –> endothermic reaction
start color #e84d39, start text, Δ, H, space, v, a, l, u, e, space, p, o, s, i, t, i, v, e, space, --, >, space, e, n, e, r, g, y, space, a, b, s, o, r, b, e, d, space, --, >, space, e, n, d, o, t, h, e, r, m, i, c, space, r, e, a, c, t, i, o, n, end text, end color #e84d39
Heat Flashcards
Start studying Heat. Learn vocabulary, terms, and more with flashcards, games, and other study tools.
Heat
4.9 30 Reviews
Two different gases are stored in separate closed containers. If both gases have a temperature of 50°C, which statement is true?
Click card to see definition 👆
d. The gas molecules in both containers have the same average kinetic energy.
Click again to see term 👆
Which statement about exothermic reactions is accurate?
Click card to see definition 👆
a. As reactants form products, the potential energy decreases.
Click again to see term 👆
1/16 Created by chelseabailey19
Terms in this set (16)
Two different gases are stored in separate closed containers. If both gases have a temperature of 50°C, which statement is true?
d. The gas molecules in both containers have the same average kinetic energy.
Which statement about exothermic reactions is accurate?
a. As reactants form products, the potential energy decreases.
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?
b. The molecules move more slowly and their average kinetic energy decreases.
Which event is endothermic?
d. the melting of ice
A baker touches a pie right after taking it out of the oven. Which statement best explains why the pie feels hot?
b. Molecules in the pie move faster than molecules in the skin, so heat is transferred to the skin.
What is thermal energy?
c. the kinetic energy of particles in a system
The diagram below shows the temperature dropping from 80°C to 20°C.
Molecules that have longer arrows are moving faster. Which statement describes what is happening in this system?
c. Kinetic energy decreases as temperature decreases.
Which answer defines exothermic reaction?
a. a process in which energy is released as heat
Which reaction is exothermic?
a. CH4 + 2O2 → CO2 + 2H2O + 891 kJ
A student touches a freshly baked cake that was taken out of the oven. Which best explains why the cake feels hot?
b. Molecules in the cake are moving faster than molecules in the skin.
An ice cube is placed on a kitchen counter. Which best describes heat flow in this situation?
d. Heat flows from the counter to the ice, causing the molecules in the counter to move more slowly.
Heat that flows by conduction is the transfer of thermal energy between substances in contact. What must occur for this to happen?
c. One system must have higher kinetic energy than the other system.
Which reaction is endothermic?
d. N2O4 + 59 kJ → 2NO2
Iron reacts with oxygen in a chemical hand-warmer. How should this reaction be categorized?
a. as an exothermic process because it releases heat
The temperature of a gas is increased. Which statement best explains the effect that this has on the motion of gas particles?
d. The average kinetic energy increases, and the particles collide more frequently.
How does the potential-energy diagram for a reaction indicate whether the reaction is endothermic or exothermic?
a. An endothermic reaction has reactants that are lower in energy than products because energy is absorbed to form the products.
Related questions
QUESTION
Helmholtz free energy equation should be used when a change in state is taking place at constant pressure
3 answers QUESTION
describe how particles behave with freezing
5 answers QUESTION
Through which material will heat be conducted the best?
15 answers QUESTION
What is the firs law of thermodynamics?
13 answers
Recommended textbook explanations
Physics for the IB Diploma Coursebook
6th Edition
K. A. Tsokos, Mark Headlee, Peter Hoeben
721 explanations
Introduction to Electrodynamics
4th Edition David J. Griffiths 584 explanations
Introduction to Quantum Mechanics
3rd Edition
Darrell F. Schroeter, David J. Griffiths
485 explanations Physics 1st Edition Walker 3,630 explanations
Sets found in the same folder
Calorimetry
14 terms chelseabailey19
Calorimetry Assignment and Quiz
14 terms katherinenguyenn
Lab: Calorimetry and Specific Heat Assignment…
7 terms katherinenguyenn
Heat
9 terms Rosa_Lopez52
Sets with similar terms
Heat Quiz
13 terms Daveon_Myles
Chemistry, heat quiz
10 terms anastasiahamilton
Heat Assignment and Quiz
14 terms katherinenguyenn
Chemistry 2 - Heat
16 terms GrimmDefience
Other sets by this creator
Photography
23 terms chelseabailey19
Government Midterm 1
84 terms chelseabailey19
The Sociology of Religion
19 terms chelseabailey19
The Sociology of Education
21 terms chelseabailey19
Other Quizlet sets
wedding anniversary
25 terms quizlette1839224
SLHS 2204 Exam 2
30 terms Alexafeder101PLUS
Vocabulary List 1
15 terms Ms_Bravo
Understanding Music for Non Major
20 terms gracemarlin
Verified questions
PHYSICS
Three processes are described below. Choose one process in which there is work done on the system The spring, Earth, and the cart are part of the system. (a) A relaxed spring rests upright on a tabletop. You slowly compress the spring. You then release the spring and it flies up several meters to its highest point. (b) A cart at the top of a smooth inclined surface coasts at increasing speed to the bottom (ignore friction). (c) A cart at the top of a smooth inclined surface slides at increasing speed to the bottom where it runs into and compresses a spring (ignore friction).
Exothermic and Endothermic Processes
Exothermic and Endothermic Processes
Thermochemistry
Exothermic and Endothermic Processes Thermochemistry Exothermic And Endothermic Processes
State the law of conservation of energy.
Define and endothermic process.
Define an exothermic process.
Make conversions involving heat units.
A camp fire is an example of basic thermochemistry. The reaction is initiated by the application of heat from a match. The reaction converting wood to carbon dioxide and water (among other things) continues, releasing heat energy in the process. This heat energy can then be used to cook food, roast marshmallows, or just keep warm when it’s cold outside.
Exothermic and Endothermic Processes
When physical or chemical changes occur, they are generally accompanied by a transfer of energy. The law of conservation of energy states that in any physical or chemical process, energy is neither created nor destroyed. In other words, the entire energy in the universe is conserved. In order to better understand the energy changes taking place during a reaction, we need to define two parts of the universe, called the system and the surroundings. The system is the specific portion of matter in a given space that is being studied during an experiment or an observation. The surroundings is everything in the universe that is not part of the system. In practical terms for a laboratory chemist, the system is the particular chemicals being reacted, while the surroundings is the immediate vicinity within the room. During most processes, energy is exchanged between the system and the surroundings. If the system loses a certain amount of energy, that same amount of energy is gained by the surroundings. If the system gains a certain amount of energy, that energy is supplied by the surroundings.
In the study of thermochemical processes, things are viewed from the point of view of the system. A chemical reaction or physical change is endothermic if heat is absorbed by the system from the surroundings. In the course of an endothermic process, the system gains heat from the surroundings and so the temperature of the surroundings decreases. The quantity of heat for a process is represented by the letter . The sign of for an endothermic process is positive because the system is gaining heat. A chemical reaction or physical change is exothermic if heat is released by the system into the surroundings. Because the surroundings is gaining heat from the system, the temperature of the surroundings increases. The sign of for an exothermic process is negative because the system is losing heat.
(A) Endothermic reaction. (B) Exothermic reaction.
Units of Heat
Heat flow is measured in one of two common units: the calorie and the joule. The joule (J) is the SI unit of energy. The calorie is familiar because it is commonly used when referring to the amount of energy contained within food. A calorie (cal) is the quantity of heat required to raise the temperature of 1 gram of water by 1°C. For example, raising the temperature of 100 g of water from 20°C to 22°C would require 100 × 2 = 200 cal.
Calories contained within food are actually kilocalories (kcal). In other words, if a certain snack contains 85 food calories, it actually contains 85 kcal or 85,000 cal. In order to make the distinction, the dietary calorie is written with a capital C.
To say that the snack “contains” 85 Calories means that 85 kcal of energy are released when that snack is processed by your body.
Heat changes in chemical reactions are typically measured in joules rather than calories. The conversion between a joule and a calorie is shown below.
We can calculate the amount of heat released in kilojoules when a 400. Calorie hamburger is digested.
Summary
Processes of heat exchange between the system and surroundings are described.
Practice
Do the problems (as many as you have time for) at the link below:
http://www.chemteam.info/Thermochem/Thermochem-WS2.html
Review
Questions
What does the law of conservation of energy say?
What is a reaction called that gives off heat?
A cake is made by mixing ingredients and placing the material in an oven for baking. What type of reaction is involved?
calorie (cal): The quantity of heat required to raise the temperature of 1 gram of water by 1°C.endothermic: Heat is absorbed by the system from the surroundings.exothermic: Heat is released by the system into the surroundings.law of conservation of energy: In any physical or chemical process, energy is neither created nor destroyed.surroundings: Everything in the universe that is not part of the system.system: The specific portion of matter in a given space that is being studied during an experiment or an observation.
Guys, does anyone know the answer?