Name: coffee cup calorimeter heat changes
Uploaded: 2020-09-03T13:38:27.000Z
Duration: 3 min 2 s
Channel: JoVE

K12 Standards

north-carolina-k-12-science-standard-course-of-study

North Carolina K-12 Science Standard Course of Study

9-12

Chemistry

Energy

PS.Chm.7.2

Constant Pressure Calorimetry

在恒压，比如一大气压下的反应，其热能的在过程 中的交换会 用焓（delta H）测量。反应中焓的变化量会体现于温度差，其被一种技术测量，为热析法。在热析法中，反应是在一个密封且校准的容器中执行，称为热量计。热量计是完全绝缘的，且阻隔任何热流进 出流动于环境中。因此，反应物及生成物之间的 热流交换其构成系统，和热量计其便是周围环境，可以被准确的计算通过监视在热量 计的温度变化。假设是放热反应，热流将会从系统释放至周围环境，且提升其温度。相反的，当是吸热反应，热流从周围环境进入系统，导致热量计的温度降低。一个基本的咖啡杯热量计 可以测量爱恆压下测 量溶液發生的焓变。热量计由两个崁合在一 起的聚苯乙烯泡沫塑料咖啡杯组成，并配有温度计及搅拌器。用鬆散的软木塞盖封闭量热计，以保持向大气压开放的 恒定压力条件。设50.0毫升1.0摩尔浓度的盐酸水溶液和 1.0摩尔浓度的氢氧化钾水溶液在热量 计中發生反应，以将溶液的温度升高6.9摄氏度。溶液（q溶液）吸收的热量等于其比热C s，每克摄氏4.18焦耳（与水相同）乘以其总质 量（m 100.0 克及温度变化量。溶液的热量是3或2.9千焦耳的 2.9乘以10的立方倍。反应的热量（q）的值相同，但是有着相反的符号。由于压力是恒定的，焓变与反应热相同。为了找到反应中 每莫耳的焓变，将焓除以盐酸的莫耳数。盐酸的莫耳数是 将其0.05公升体积乘以 一莫耳莫耳数得出的。因此，负2.9千焦耳除以0.050莫耳可 得到负58公斤 焦耳/莫耳。

<ol>
	<li>班纳，M. 萨利姆。"恒压量热法加热器。"化学教育杂志 63，第 11 期（1986）:997。</li>
	<li>"经济、安全、坚固的学生量热仪。"化学教育杂志 71，第 4 期（1994）:333。</li>
	<li>斯坦库斯、约翰 J. 和詹妮弗 D. 卡拉威。"用制造的烧杯量热仪取代咖啡杯量热仪。"化学教育杂志 88，第 12 期（2011）:1730-1731. 
	 </li>
</ol>

恒压量热法

量热法是一种用于测量化学或物理过程中涉及的热量或测量传递至物质或从物质传递的热量的技术。热量通过称为热量计的已校准且绝缘的设备进行交换。量热实验基于这样的假设，即绝缘量热仪与外部环境之间没有热交换。绝缘良好的量热计可防止热量在量热计与其外部环境之间传递，从而有效地限制了“周围环境”。量热仪中的非系统组件（以及量热仪本身）。这样可以准确确定化学过程中涉及的热量，例如食品的能量含量。
 
 通过量热仪测量的温度变化可用于得出所研究过程传递的热量。在量热仪中，系统定义为发生化学或物理变化的一种或多种物质，或者换句话说，是反应，并且周围环境都是所有其他物质，包括溶液和量热仪中提供热量的任何其他成分进入系统或从系统吸收热量。
 
 在讨论化学反应的量热法之前，请考虑一个更简单的示例，它说明了量热法背后的核心思想。假设将高温的高温金属放在诸如冷水之类的低温物质中。热量将从铁水流到水中。金属的温度将降低，水的温度将升高，直到两种物质具有相同的温度-即达到热平衡为止。如果这在热量计中发生，则所有热量都在两种物质之间传递，而其外部环境不会吸收或损失热量。在这些理想情况下，净热变化为零：
 
 <img alt="Eq1" src="https://www.jove.com/files/core/CDNSource/lessons/798/798_Equations-01.png" style="height: 40px;" />
 
 可以重新安排这种关系，以表明金属获得的热量等于水所散失的热量：
 
 <img alt="Eq2" src="https://www.jove.com/files/core/CDNSource/lessons/798/798_Equations-02.png" style="height: 40px;" />
 
 因此，两种物质的热量（变化）大小相同。负号仅表示 q metal 和 q 水在热流方向上相反（增益或损耗），但未表示 q 值的算术符号（根据定义，该值取决于所讨论的问题是变热还是变热）。在所描述的特定情况下， q metal 是负值，而 q 水是正值，因为热量是从金属转移到水中。
 
 使用量热法确定化学反应中涉及的热量时，适用相同的原理。量热仪吸收的热量通常足够小，以至于通常可以忽略不计，并且量热仪可以最大程度地减少与外界环境的能量交换。当热量计中的溶液发生放热反应时，反应产生的热量会被溶液吸收，从而使温度升高。当发生吸热反应时，所需的热量会从溶液的热能中吸收，从而降低溶液的温度。温度变化（Δ T ）以及比热（ c soln ）和溶液质量（ m soln ），然后可以用来计算这两种情况下的热量（ q soln ）。
 
 <img alt="Eq3" src="https://www.jove.com/files/core/CDNSource/lessons/798/798_Equations-03.png" style="height: 40px;" />
 
 简单的量热仪＆mdash;称为咖啡杯量热仪-由两个嵌套的聚苯乙烯杯构成，并用一个松散的盖子封闭。咖啡杯量热仪用于测量溶液（主要是水溶液）中发生的反应热，其体积变化不大或变化很小。由于在化学反应过程中既不会产生能量也不会破坏能量，因此在反应（“系统”）中产生或消耗的热量 q rxn ，以及吸收的热量或解决方案（“周围环境”）丢失的 q soln 必须加起来为零：
 
 <img alt="Eq4" src="https://www.jove.com/files/core/CDNSource/lessons/798/798_Equations-04.png" style="height: 40px;" />
 
 这意味着反应中产生或消耗的热量等于溶液吸收或损失的热量：
 
 <img alt="Eq5" src="https://www.jove.com/files/core/CDNSource/lessons/798/798_Equations-05.png" style="height: 40px;" />
 
 咖啡杯量热仪是恒压量热仪，测得的反应热等于焓变。
 
 <img alt =“ Eq6” src =“ https://www.jove.com/files/core/CDNSource/lessons/798/798_Equations-06.png” style =“ height：40px ;“ /> 
 
 本文改编自<a href="https://openstax.org/books/chemistry-2e/pages/5-2-calorimetry"> Openstax，化学2e，第5.2节：量热法</ a>。

量热法是一种用于测量化学或物理过程中所涉及的热量，或测量传递至某一物质或从该物质传递出的热量的技术。

Education

教育

JoVE Core

化学

Thermochemistry

热化学

KEY TERMS AND CONCEPTS

关键术语与概念

coffee cup calorimeter heat changes

Coffee cup calorimetry measures heat changes in reactions and physical changes using an insulated calorimeter. The calorimeter is calibrated and designed to limit heat exchange with the outside environment. That makes it possible to measure the heat taken in or released by a substance more accurately, including the energy content of foods.

In calorimetry, the system is the substance or substances undergoing change. The surroundings are everything else inside the calorimeter, including the solution and any other components that can give heat to the system or absorb heat from it. The measured temperature change is then used to calculate the heat transferred in the process under study.

A simple example helps show the idea. If a hot piece of metal is placed in cool water, heat flows from the metal to the water until both reach thermal equilibrium, or the same temperature. In an ideal calorimeter, no heat is gained or lost by the external environment, so the heat lost by the metal equals the heat gained by the water. The two heat values have the same magnitude, but they point in opposite directions of heat flow.

The same rules apply when a chemical reaction happens in solution. For an exothermic reaction, the reaction gives off heat, and the solution absorbs it, so the solution temperature rises. For an endothermic reaction, the reaction absorbs heat from the solution, so the solution temperature falls. The temperature change, along with the solution mass and specific heat, can be used to find the heat involved.

A coffee cup calorimeter is a simple constant-pressure calorimeter made from two nested polystyrene cups with a loose-fitting lid. It is used for reactions in solution, mostly aqueous solutions, when there is little or no volume change. In this setup, the heat of the reaction, q rxn, and the heat of the solution, q soln, add up to zero. That means the heat released or absorbed by the reaction matches the heat gained or lost by the solution. Because the pressure stays constant, the measured heat change is the enthalpy change.

Coffee Cup Calorimeter Heat Changes

energy basics

How Energy Changes in Chemical Reactions

Chemical reactions change matter and energy at the same time. A match lighting is a simple example. These energy changes are part of everyday life and appear in food, fuels, and industry. Food provides energy through metabolic reactions. The macronutrients in food break down and help keep the body functioning. Fuels such as gasoline, natural gas, and coal are burned to produce energy for transportation, heating, and electricity generation. Industrial chemical reactions also use large amounts...

first law of thermodynamics

Energy Conservation and Internal Energy

Energy conservation describes how energy changes form during chemical and physical changes. Energy can be converted from one form into another, but the energy present before a change still exists in some form after the change is complete. This is the law of conservation of energy. It says energy can neither be created nor destroyed. The law of conservation of matter also applies during chemical change. In most chemical reactions, the total amount of matter does not show a detectable change.

internal energy

Internal Energy, Heat, and Work

Internal energy is the total of all possible kinds of energy in a substance. It is often written as U, and sometimes as E. For a system that changes energy, the important value is the change in internal energy, or ΔU. ΔU is the difference between the final internal energy and the initial internal energy. The exact values of U final and U initial are usually not known, but the first law of thermodynamics only requires ΔU. A positive ΔU means the system gained energy from the surroundings. A...

quantifying heat

Heat Transfer and Specific Heat

Heat transfer and specific heat explain how thermal energy moves and how materials respond to it. Thermal energy is the kinetic energy linked to the random motion of atoms and molecules. Temperature is a measure of how hot or cold a substance is, and it depends on how much thermal energy those particles have. When atoms and molecules move or vibrate faster, their average kinetic energy is higher. That means the object has more thermal energy and a higher temperature. When they move more...

quantifying work

Pressure-Volume Work in Chemistry

Pressure-volume work shows how gas volume changes can transfer energy in chemistry. As a system changes, its internal energy may change too. Energy can move between the system and the surroundings through heat and work. Internal energy, heat, and work are related by an energy equation. Heat depends on a measured temperature change. Work depends on a measured change in volume called pressure-volume work. Work can be defined as a force acting through a distance. Pressure-volume work, also...

enthalpy

Enthalpy and Heat at Constant Pressure

Enthalpy describes heat changes in chemical and physical processes. Chemists use the symbol H for enthalpy. It is defined as a system’s internal energy, E, plus the product of pressure, P, and volume, V. Enthalpy is a state function, so only changes in enthalpy can be measured, not the enthalpy of a substance by itself. For many reactions, the pressure stays constant. Under those conditions, the enthalpy change, ΔH, can be written in a way that includes pressure-volume work. The term PΔV...

thermochemical equations

Heat Changes in Chemical Equations

Heat changes in chemical equations show how much energy a reaction releases or absorbs. At constant pressure, the enthalpy of reaction, or ΔHrxn, is equal to the heat exchanged with the surroundings, qp. Because this value depends on how much reactant takes part, it is an extensive property. The size and sign of ΔHrxn also depend on the reaction itself and on the physical states of the substances involved. An exothermic reaction has a negative ΔHrxn value, while an endothermic reaction has a...

constant pressure calorimetry

Coffee cup calorimetry measures heat changes in reactions and physical changes using an insulated calorimeter. The calorimeter is calibrated and designed to limit heat exchange with the outside environment. That makes it possible to measure the heat taken in or released by a substance more accurately, including the energy content of foods. In calorimetry, the system is the substance or substances undergoing change. The surroundings are everything else inside the calorimeter, including the...

constant volume calorimetry

Bomb Calorimeter Heat Measurement

Bomb calorimetry measures the heat released by reactions that produce a lot of energy, especially combustion reactions. A coffee cup calorimeter works at constant pressure and is useful for reactions in solution. A bomb calorimeter works at constant volume and is used for reactions that make large amounts of heat and gaseous products. The word "bomb" refers to the strong, explosive force some reactions can have. In a bomb calorimeter, the volume does not change, so 94V = 0. That means the...

hess's law

Calculating Reaction Heat with Hess's Law

Calculating reaction heat with Hess's law lets chemists find enthalpy changes without measuring every reaction directly. Some reactions are hard or impossible to test in the lab. Even when a reaction can be measured, it is often easier to calculate the heat change from other known enthalpy values. Hess's law says that if a process can be written as the sum of several stepwise processes, the enthalpy change for the total process equals the sum of the enthalpy changes for the steps. This works...

standard enthalpy of formation

Using Standard Enthalpy Values in Chemistry

Enthalpy changes are often listed for reactions that start and end under the same conditions. Chemists use a standard state as a reference set of conditions for comparing properties. In IUPAC terms, the standard state means 1 bar of pressure and 1 M solutions, but it does not set a temperature. Many thermochemical tables still use 1 atm as the reference pressure. Because the difference between 1 bar and 1 atm is very small, enthalpy change usually stays almost the same. A superscripted o in...

enthalpies of reaction

Calculating reaction heat with Hess's law uses standard enthalpies of formation to find the enthalpy change of a reaction. When the formation values for the reactants and products are known, the overall reaction can be broken into simpler stepwise reactions. This approach helps show how the heat change for the full reaction is built from smaller parts. First, the reactants are thought of as being decomposed into their component elements. The enthalpy change for this step is proportional to the...

key terms and concepts

Explore how a coffee cup calorimeter measures heat changes in solutions, from thermal equilibrium to exothermic and endothermic reactions at constant pressure.

Coffee Cup Calorimeter Heat Changes | JoVE K12

chemistry

JoVE Core 化学通过简单明了且通俗易懂的动画视频课程，将普通化学概念带入到现实生活当中。此外，在科学家行动视频中，我们演示了在实验室中进行的经典和原始研究实验。

Matter and its Interactions

PS.Chm.4.1

Louisiana Student Standards for Science

High School

HS-PS3-4

ohios-learning-standards-and-model-curriculum

Ohio’s Learning Standards and Model Curriculum

Interactions Of Matter

Chemical reactions

Tennessee Academic Standards

CHEM1.PS3.1

CHEM1.PS3.2

Virginia  Standards of Learning

HIgh School

CH.7

CH.7.a

Arizona Science Standards

Physical Science

HS+Phy.P4

HS+Phy.P4U1.6

Texas Essential Knowledge and Skills

CHEM.13

CHEM.13.B

Georgia Standards of Excellence

SC5.

heat-changes-in-chemical-and-physical-processes

Heat Changes in Chemical and Physical Processes

Classifying Matter by State

Chemistry is the study of matter and the changes it undergoes. Matter is anything that has mass and occupies space. Matter is all around us; the air, ...

Classifying Matter by Composition

Matter: Pure Substances and Mixtures
According to its composition, the matter can be classified into two broad categories &mdash; pure substances and ...

physical-and-chemical-properties-of-matter

Physical and Chemical Properties of Matter

The characteristics that enable us to distinguish one substance from another are called properties.

Physical Properties of Matter

A physical property is ...

molecular-comparison-of-gases-liquids-and-solids

Molecular Comparison of Gases, Liquids, and Solids

Particles in a solid are tightly packed together (fixed shape) and often arranged in a regular pattern; in a liquid, they are close together with no ...

Intermolecular vs Intramolecular Forces

Intermolecular forces (IMF) are electrostatic attractions arising from charge-charge interactions between molecules. The strength of the intermolecular ...

Intermolecular Forces

Atoms and molecules interact through bonds (or forces): intramolecular and intermolecular. The forces are electrostatic as they arise from interactions ...

comparing-intermolecular-forces-melting-point-boiling-point

Comparing Intermolecular Forces: Melting Point, Boiling Point, and Miscibility

Intermolecular forces are attractive forces that exist between molecules. They dictate several bulk properties, such as melting points, boiling points, ...

surface-tension-capillary-action-and-viscosity

Surface Tension, Capillary Action, and Viscosity

Surface Tension
The various IMFs between identical molecules of a substance are examples of cohesive forces. The molecules within a liquid are surrounded ...

States of Matter and Phase Changes

The internal energy of a substance&#8212;the total kinetic energy of all its molecules and the potential energy of their associated forces&#8212;depends ...

Phase Transitions

Whether solid, liquid, or gas, a substance&#39;s state depends on the order and arrangement of its particles (atoms, molecules, or ions). Particles in the ...

phase-transitions-vaporization-and-condensation

Phase Transitions: Vaporization and Condensation

The physical form of a substance changes on changing its temperature. For example, raising the temperature of a liquid causes the liquid to vaporize ...

Vapor Pressure

When a liquid vaporizes in a closed container, gas molecules cannot escape. As these gas phase molecules move randomly about, they will occasionally ...

Clausius-Clapeyron Equation

The equilibrium between a liquid and its vapor depends on the temperature of the system; a rise in temperature causes a corresponding rise in the vapor ...

Phase Transitions: Melting and Freezing

Heating a crystalline solid increases the average energy of its atoms, molecules, or ions, and the solid gets hotter. At some point, the added energy ...

phase-transitions-sublimation-and-deposition

Phase Transitions: Sublimation and Deposition

Some solids can transition directly into the gaseous state, bypassing the liquid state, via a process known as sublimation. At room temperature and ...

Heating and Cooling Curves

When a substance&#8212;isolated from its environment&#8212;is subjected to heat changes, corresponding changes in temperature and phase of the substance ...

Phase Diagrams

A phase diagram combines plots of pressure versus temperature for the liquid-gas, solid-liquid, and solid-gas phase-transition equilibria of a substance. ...

Use models to explain how changes in energy affect the arrangement and movement of the particles in solids, liquids, and gases, as well as the relative strengths of their intermolecular forces.

PS.Chm.7.1

Energy Basics

Chemical reactions, such as those that occur when you light a match, involve changes in energy as well as matter.

Chemical changes and their accompanying ...

First Law of Thermodynamics

Energy Conservation

Energy can be converted from one form into another, but all of the energy present before a change occurs always exists in some form ...

Internal Energy

The total of all possible kinds of energy present in a substance is called the internal energy (U), sometimes symbolized as E. Suppose a system with ...

Quantifying Heat

Thermal Energy&#160;

Microscopically, thermal energy is the kinetic energy associated with the random motion of atoms and molecules. Temperature is a ...

Quantifying Work

As a system undergoes a change, its internal energy can change, and energy can be transferred from the system to the surroundings, or from the ...

Enthalpy

Chemists ordinarily use a property known as enthalpy (H) to describe the thermodynamics of chemical and physical processes. Enthalpy is defined as the sum ...

Thermochemical Equations

For a chemical reaction (the system) carried out at constant pressure &ndash; with the only work done caused by expansion or contraction &ndash; the ...

Calorimetry is a technique used to measure the amount of heat involved in a chemical or physical process or to measure the heat transferred to or from a ...

Constant Volume Calorimetry

Calorimeters are useful to determine the heat released or absorbed by a chemical reaction. Coffee cup calorimeters are designed to operate at constant ...

using-differential-scanning-calorimetry-to-measure-changes-in-enthalpy

Using Differential Scanning Calorimetry to Measure Changes in Enthalpy

Source: Laboratory of Dr. Terry Tritt &#8212; Clemson University
Differential Scanning Calorimetry (DSC) is a method of thermodynamic analysis based on ...

Hess's Law

There are two ways to determine the amount of heat involved in a chemical change: measure it experimentally, or calculate it from other experimentally ...

Standard Enthalpy of Formation

Enthalpy changes are typically tabulated for reactions in which both the reactants and products are at the same conditions. A standard state is a commonly ...

Enthalpies of Reaction

Hess&rsquo;s law can be used to determine the enthalpy change of any reaction if the corresponding enthalpies of formation of the reactants and products ...

Use mathematics and computational thinking to execute simple calorimetric calculations based on the Law of Conservation of Energy.

definition-measurement-pressure-atmospheric-pressure-barometer

Definition and Measurement of Pressure: Atmospheric Pressure, Barometer, and Manometer

Gas pressure is caused by force exerted by gas molecules colliding with the surfaces of objects. Although the force of each collision is very small, any ...

gas-laws-boyle-s-gay-lussac-charles-avogadro-s-and-ideal-gas-law

Gas Laws: Boyle's, Gay-Lussac, Charles', Avogadro's, and Ideal Gas Law

Through experiments, scientists established the mathematical relationships between pairs of variables, such as pressure and temperature, pressure and ...

applications-of-the-ideal-gas-law-molar-mass-density-and-volume

Applications of the Ideal Gas Law: Molar Mass, Density, and Volume

The volume occupied by one mole of a substance is its molar volume. The ideal gas law, PV = nRT, &nbsp;suggests that the volume of a given quantity of gas ...

mixtures-of-gases-dalton-s-law-of-partial-pressures-and-mole-fractions

Mixtures of Gases: Dalton's Law of Partial Pressures and Mole Fractions

Unless individual gases chemically react with each other, the individual gases in a mixture of gases do not affect each other&rsquo;s pressure. Each gas ...

chemical-stoichiometry-gases-using-ideal-gas-law-to-determine

Chemical Stoichiometry and Gases: Using Ideal Gas Law to Determine Moles

Chemical stoichiometry describes the quantitative relationships between reactants and products in chemical reactions.

In addition to measuring quantities ...

basic-postulates-kinetic-molecular-theory-particle-size-energy

Basic Postulates of Kinetic Molecular Theory: Particle Size, Energy, and Collision

The ideal-gas equation, which is empirical, describes the behavior of gases by establishing relationships between their macroscopic properties. For ...

kinetic-molecular-theory-gas-laws-explain-properties-gas

Kinetic Molecular Theory and Gas Laws Explain Properties of Gas Molecules

The test of the kinetic molecular theory (KMT) and its postulates is its ability to explain and describe the behavior of a gas. The various gas laws ...

kinetic-molecular-theory-molecular-velocities-temperature-kinetic

Kinetic Molecular Theory: Molecular Velocities, Temperature, and Kinetic Energy

The kinetic molecular theory qualitatively explains the behaviors described by the various gas laws. The postulates of this theory may be applied in a ...

behavior-gas-molecules-molecular-diffusion-mean-free-path

Behavior of Gas Molecules: Molecular Diffusion, Mean Free Path, and Effusion

Although gaseous molecules travel at tremendous speeds (hundreds of meters per second), they collide with other gaseous molecules and travel in many ...

real-gases-effects-intermolecular-forces-molecular-volume-deriving

Real Gases: Effects of Intermolecular Forces and Molecular Volume Deriving Van der Waals Equation

Thus far, the ideal gas law, PV = nRT, has been applied to a variety of different types of problems, ranging from reaction stoichiometry and empirical and ...

Ideal Gas Law

Source: Laboratory of Dr. Andreas Z&#252;ttel - Swiss Federal Laboratories for Materials Science and Technology
The ideal gas law describes the behavior ...

Derivation of the Ideal Gas Law
Gases are a fundamental state of matter. A gas is a collection of molecules that have a significant distance between their ...

Source: Smaa Koraym at Johns Hopkins University, MD, USA

	Preparation of the LaboratoryExpand
	Here, we show the laboratory preparation for 10 students ...

Source: Smaa Koraym at Johns Hopkins University, MD, USA

	Determining the Mass of the Unknown LiquidExpand
	According to the ideal gas law for a given ...

Use mathematics and computational thinking to explain the relationships among pressure, temperature, volume, and quantity of gas, both qualitatively and quantitatively.

PS.Chm.7.3

Understand the relationship among pressure, temperature, volume, and phase.

Coffee Cup Calorimeter Heat Changes

Description

Transcript

Tags

More videos by Standards