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

大気圧のような一定の圧力下で 行われる化学反応では その過程で交換される熱量は エンタルピーΔHの変化として 測定されます 反応のエンタルピーの変化は 温度の変化として現れ 熱量測定と呼ばれる 技術を用いて測定されます 熱量測定では 反応は熱量計と呼ばれる 密閉された校正済みの 容器の中で行われます 熱量計は十分に絶縁されており それ自体と環境との間の熱の 移動を防ぎます このように システムを 構成する反応物と 生成物との間で 交換された熱量は 環境となる熱量計の 温度変化を 測定することで正確に 計算することができます 反応が発熱性であれば 系から周囲に熱が流れ 温度が上昇します 逆に 反応が吸熱性の場合は 熱が周囲から系内に流れ込み 熱量計の温度が低下します 簡易コーヒーカップ式熱量計は 溶液中で発生する 反応のエンタルピーの変化を 一定の圧力条件で測定します 熱量計は 一緒に入れ子になった 温度計と攪拌機を備え 2つの 発泡スチロールコーヒーカップで 構成されています 熱量計は 大気に開放されている 一定の圧力の 条件を維持するために 緩いフィットコルク蓋で 閉じられています 熱量計内に 1.0モルの塩酸水溶液と 1.0モルの 水酸化カリウム水溶液を 50.0ミリリットルずつ 入れて反応させ 溶液の温度を 6.9℃上昇させたとします この溶液が吸収する熱は その比熱であるC s の 摂氏温度あたり 4.18ジュール/gに その全質量である m-100.0グラムと 温度の変化を かけたものに等しくなります 溶液の熱は 2.9x10の3乗 キロジュールになります Ｑ反応の熱は同じ値ですが 符号は逆です 圧力が一定なので エンタルピーの変化は 反応の熱と同じです 1モルあたりの反応の エンタルピー変化を求めるには エンタルピーを 塩酸のモル数で割ります 塩酸のモル数は リットル単位の 体積-0.05 Lに モル濃度1 Mを乗じて求めます つまり負の2.9キロジュールを 0.050モルで割ると 1モルあたり負の 58キロジュールが得られます

<ol>
	<li>「定圧熱量測定用ヒーター」 Journal of Chemical Education 63, no. 11 (1986): 997.</li>
	<li>「経済的で、安全で、頑丈な学生用熱量計」 Journal of Chemical Education 71, no. 4 (1994): 333.</li>
	<li>「コーヒーカップ熱量計を製造されたビーカー熱量計に置き換える」 Journal of Chemical Education 88, no. 12 (2011): 1730-1731. 
	 </li>
</ol>

一定圧力の熱量測定

熱量測定は、化学的または物理的なプロセスに含まれる熱の量を測定したり、物質との間で伝達される熱を測定するために使用される技術です。 熱は、熱量計と呼ばれる、校正および断熱された装置で交換されます。 熱量測定の実験は、断熱された熱量計と外部環境との間に熱交換がないことを前提としています。 十分に断熱された熱量計は、熱量計とその外部環境間の熱の移動を防ぎます。これにより、 " 環境 " が熱量計内の非システム構成要素（および熱量計自体）に効果的に制限されます。 これにより、食品のエネルギー含有量など、化学プロセスに関わる熱を正確に測定することができます。  
 
 熱量計によって測定される温度変化は、検討中のプロセスによって伝達された熱量を算出するために使用されます。 熱量計では、システムとは物質または化学物質または物理的変化中の物質、つまり反応と定義されます。 また、環境とは、溶液や熱量計内の他の構成要素など、システムに熱を供給するか、システムから熱を吸収するものも含め、その他のものすべてにあたります。 
 
 化学反応の熱量測定について説明する前に、熱量測定の基本的な考え方を示す簡単な例を考えてみましょう。 高温の金属部分が低温の物質（冷却水など）に置かれているとします。 熱は熱い金属から水に流れます。 金属の温度が下がり、2 つの物質が熱平衡に達するまで、水の温度が上昇し、 2 つの物質の温度が同じになります。熱量計でこのようなことが起こった場合、熱はすべて 2 つの物質間で移動され、外部環境によって熱が得られたり失われることはありません。 このような理想的な状況では、正味の熱交換はゼロです。 
 
 <img alt=""Eq1"" src=""https://www.jovecore.com/CDNSource/lessons/798/798_Equations-01.png"" style=""height: 40px;"" />
 
 この関係は、金属が得た熱が水物質によって失われた熱と同等であることを示すように、次のように再配置できます。 
 
 <img alt=""Eq2"" src=""https://www.jovecore.com/CDNSource/lessons/798/798_Equations-02.png"" style=""height: 40px;"" />
 
 したがって、熱の大きさ（変化）は両方の物質で同じです。 負の符号は単にqmetal とqwater が熱の流れ（得たり失う）の方向と反対であることを示しているだけですが、いずれの q 値の符号（問題の物質が定義ごとに熱を得るか失うかによって決まる）も示していません。 具体的な状況では、 qmetal は負の値であり、 qwater は正の値です。これは熱が金属から水に移動したためです。 
 
 化学反応に関与する熱を計算するために熱量計を使用する場合は、同じ原理が適用されます。 熱量計が吸収する熱量は、ほとんど無視できるほど小さく、熱量計は外部環境とのエネルギー交換を最小限に抑えます。 熱量計の溶液中で発熱反応が発生すると、反応によって生成される熱は溶液に吸収され、溶液の温度が上昇します。 吸熱反応が発生すると、必要な熱が溶液の熱エネルギーから吸収され、温度が下がります。 温度変化（ Δ T ）と、比熱（csoln ）および溶液質量（ msoln ）を使用して、どちらの場合も熱量（ qsoln ）を計算できます。 
 
 <img alt=""Eq3"" src=""https://www.jovecore.com/CDNSource/lessons/798/798_Equations-03.png"" style=""height: 40px;"" />
 
 コーヒーカップ熱量計と呼ばれる単純な熱量計は、緩めの蓋で閉じた 2 つのポリスチレン製カップで構成されています。 コーヒーカップ熱量計は、溶液中で発生する反応の熱を測定するために使用され（主に水溶液）、量の変化がまったく、またはほとんどありません。 化学反応中にエネルギーが生成または分解されることはないため、反応で生成または消費される熱（「システム」）、 qrxn 、および溶液によって吸収または失われる熱（「環境」）、 qsoln は、ゼロになるまで加える必要があります。 
 
 <img alt=""Eq4"" src=""https://www.jovecore.com/CDNSource/lessons/798/798_Equations-04.png"" style=""height: 40px;"" />
 
 つまり、反応で生成または消費される熱の量は、溶液によって吸収または失われる熱の量と等しくなります。

熱量測定は、化学的または物理的プロセスに関与する熱量を測定するために使用される技術です。または、熱量測定器との間で伝達される熱を測定するために使用されます...

Education

JoVE Core

化学

Thermochemistry

熱化学

KEY TERMS AND CONCEPTS

主要用語と概念

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...

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internal energy

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quantifying work

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enthalpy

Enthalpy and Heat at Constant Pressure

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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

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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...

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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 化学は、簡潔で理解しやすいアニメーションビデオレッスンを使用して、一般的な化学の概念を生き生きとしたものにします。さらに、活動する科学者のビデオでは、現在世界中の実験室で行われている古典的そして独創的な研究・実験をお見せします。

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.

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Coffee Cup Calorimeter Heat Changes

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