Determination Of Specific Heat Of Given Liquid By Method Of Mixture

Determination Of Specific Heat Of Given Liquid By Method Of Mixture

Vishal kumarUpdated on 02 Jul 2025, 07:13 PM IST

The determination of the specific heat of a given liquid by the method of mixtures is a fundamental experiment in thermodynamics. This method involves mixing a known mass of the liquid at a certain temperature with another substance, typically water, at a different temperature. By measuring the final equilibrium temperature of the mixture, the specific heat of the liquid can be calculated. This experiment is essential in understanding heat transfer and energy conservation.

This Story also Contains

  1. Procedure
  2. Observations
  3. Calculations
  4. Result
  5. Solved Examples Based on Determination Of Specific Heat Of Given Liquid By Method Of Mixture
  6. Summary
Determination Of Specific Heat Of Given Liquid By Method Of Mixture
Determination Of Specific Heat Of Given Liquid By Method Of Mixture

In real life, the specific heat of liquids plays a crucial role in various applications. For instance, it helps in designing heating and cooling systems, such as radiators and air conditioners, where knowledge of how different fluids absorb and release heat is vital. Another example is in culinary arts, where chefs use the specific heat of water to determine cooking times and temperatures for different recipes, ensuring consistent and precise results.

Aim
To determine the specific heat capacity of a given liquid by method of mixtures.

Apparatus
A hypsometer, calorimeter, stirrer, a lid and outer jacket, given solid of known specific heat capacity in powder form or in small pieces, balance, weight box, two half-degree thermometer, Liquid whose specific heat capacity is to be measured, clamp stand.

Theory
In a hypsometer, the solid is heated uniformly above room temperature up to a fixed temperature and then solid is added to the given liquid in the calorimeter.
Heat lost by solid = Heat gained by the water and calorimeter.

Procedure

1. Put two thermometers A and B in a beaker containing the given liquid and note their reading. Take one of them, say A to be standard and find the correction to be applied to the other, say B.
2. Put thermometer B in a copper tube of a hypsometer containing the powder of the given solid. Put sufficient given liquid in a hypsometer and placed it on a burner.
3. Weigh the calorimeter with a stirrer and lid over it by the physical balance. Record it.

4. Fill about half of the calorimeter with the given liquid at about temperature 5 to 8oC below room temperature. Now, weigh it again and record it.
5. Heat the hypsometer for about 10 minutes till the temperature of the solid remains steady.
6. Note the temperature of the given liquid in the calorimeter. Now, transfer the solid from the hypsometer to the calorimeter quickly. Stir the contents and record the final temperature of the mixture.
7. Remove the thermometer A from the calorimeter and weigh the calorimeter with its contents and lid.

Observations

1. Reading of thermometer A=TA=0C
2. Reading of thermometer B=TB=..0C
3. Correction applied in w.r.t A=(TATB)=0C
4. Mass of calorimeter and stirrer m= g
5. Water equivalent of calorimeter =w=m×0.095= g
6. Specific heat of copper calorimeter =0.095cal/g
7. Mass of calorimeter + stirrer + lid =m1=.g
8. Mass of calorimeter + stirrer + lid + cold water =m2=.. g
9. Steady temperature of hot solid =TS=.C
10. Corrected temperature of hot solid T=TS(TATB)=..C
11. Temperature of given liquid =t=..C
12. Temperature of mixture =θ=..C
13.
Mass of calorimeter, stirrer, lid, given liquid and solid =m3=g

Calculations

1. Mass of given liquid =m2m1=g
2. Mass of hot solid =m3m2=.. g
3. Rise of the temperature of given liquid and calorimeter =θt=.C
4. Fall in temperature of solid =Tθ=.C
5. Heat gain by calorimeter, given liquid and stirrer =[ω+(m2m1)(θt)]=
6. Heat lost by solid =(m3m2)×C×(Tθ)=
7. Here, C is the specific heat of the solid to be calculated.

According to the principle of calorimeter, heat lost = heat gained

(m3m2)×C×(Tθ)=[ω+(m2m1)(θt)]C=[ω+(m2m1)(θt)](m3m2)(Tθ)]= callg C

Result

Specific heat of given liquid by method of mixture is .. . calg 1c1

Solved Examples Based on Determination Of Specific Heat Of Given Liquid By Method Of Mixture

Example 1: Two liquids of equal volume are thoroughly mixed. If their specific heats are c1 and c2 temperature Θ1,Θ2 and densities d1,d2 respectively. What is the final temperature of the mixture?

1) d1c1Θ1+d2c2Θ2d1Θ1+d2Θ2
2) c1Θ1+c2Θ2d1c1+d2c2
3) d1Θ1+d2Θ2c1Θ1+c2Θ2
4) d1c1Θ1+d2c2Θ2d1c1+d2c2

Solution:

Θ=m1c1Θ1+m2c2Θ2m1c1+m2c2m1=d1v,m2=d2vΘ=d1c1Θ1+d2Θ2c2d1c1+d2c2Hence, the answer is the option 4.

Example 2: A metal block of mass m1=0.5 kg and initial temperature T1=300 K is placed in a container of water of mass m2=2.0 kg and initial temperature. T2=280 K. After some time, both the metal block and water come to a common final temperature Tf=290 K. Given that the specific heat of the metal is cmetal =400 J/kgK and the specific heat of water is cwater =4186 J/kgK calculate the specific heat capacity of the metal block.

1) 41860 kJ/kgK.
2) 41860 J/kgK.
3) 41860 kJ/kgK.
4) 21860 J/kgK.

Solution:

Given:

  • - Mass of metal block m1=0.5 kg
    - The initial temperature of the metal block T1=300 K
    - Mass of water m2=2.0 kg
    - The initial temperature of the water T2=280 K
    - Final temperature Tf=290 K
    - Specific heat of metal cmetal =400 J/kgK
    - Specific heat of water cwater =4186 J/kgK

    Step 1: Calculate the heat gained by the metal block (Qmetal ) :

    Qmetal =m1cmetal (TfT1)Qmetal =0.5 kg400 J/kgK(290 K300 K)
    Step 2: Calculate the heat lost by the water (Qwater ) :

    Qwater =m2cwater (T2Tf)Qwater =2.0 kg4186 J/kgK(280 K290 K)

Step 3: Since the heat gained by the metal is equal to the heat lost by the water at thermal equilibrium:

Qmetal =Qwater

0.5 kg400 J/kgK(290 K300 K)=2.0 kg4186 J/kgK(280 K290 K)
Step 4: Solve for the specific heat capacity of the metal (cmetal ) :

cmetal =2.0 kg4186 J/kgK(280 K290 K)0.5 kg(290 K300 K)
Step 5: Calculate Cmetal :

cmetal =41860 J/kgK
The specific heat capacity of the metal block is 41860 J/kgK.

Hence, the answer is the option (1).

Example 3: A metal block of mass m1=0.2 kg and specific heat cmetal =500 J/kgK is placed in a container of water of mass m2=1.0 kg and specific heat Cwater =4186 J/kgK. Both the metal block and water come to a common final temperature Tf=320 K. Calculate the initial temperature T1 of the metal block.

1) 320 K

2) 340 K

3) 390 K

4) 230 K

Solution:

Given:

Mass of metal block m1=0.2 kg
Specific heat of metal Cmetal =500 J/kg.K
Mass of water m2=1.0 kg
Specific heat of water Cwater =4186 J/kgK
Final temperature Tf=320 K
Step 1: Calculate the heat gained by the metal block ( Qmetal ) to reach the final temperature Tf:

Qmetal =m1cmetal (TfT1)
Step 2: Calculate the heat gained by the water (Qwater) to reach the final temperature Tf :

Qwater =m2cwater (TfT1)
Step 3: Since both the metal block and water come to the same final temperature Tf, the heat gained by the metal is equal to the heat gained by the water:
Qmetal =Qwater m1cmetal (TfT1)=m2cwater (TfT1)
Step 4: Solve for the initial temperature T1 of the metal block:

m1cmetal (TfT1)=m2cuater (TfT1)0.2 kg500 J/kgK(320 KT1)=1.0 kg4186 J/kgK(320 KT1)
Step 5: Solve for T1 :

0.2 kg500 J/kgK(320 KT1)=1.0 kg4186 J/kgK(320 KT1)100(320T1)=4186(320T1)100320100 T1=41863204186 T132000100 T1=13395204186 T14086 T1=1307520T1=13075204086

Step 6: Calculate T1:

T1320.33 K
The initial temperature T1 of the metal block is approximately 320.33 K .

The initial temperature T1 of the metal block is approximately 320.33 K.

Hence, the answer is the option (1).

Example 4: In an experiment, a piece of metal is heated to a high temperature and then placed in an insulated container with water. The initial temperature of the water is Ti=25C and the initial temperature of the metal is Tm=150C, After thermal equilibrium is reached, the final temperature of the water and metal mixture is Tf=30C The mass of the metal is m=0.2 kg, and the mass of water is M=0.5 kg. The specific heat of water is cw=4200 J/kgC. The specific heat cm of the metal is:

1) 100 J/kgC
2) 250.5 J/kgC
3) 437.5 J/kgC
4) 500 J/kgC

Solution:

The heat lost by the hot metal is equal to the heat gained by the cold water. This can be expressed using the formula:
mcm(TmTf)=Mcw(TfTi)
Given:

m=0.2 kgTm=150CM=0.5 kgTi=25CTf=30Ccw=4200 J/kgC
Solve for cm :

cm=Mcw(TfTi)m(TmTf)
Substitute the given values:

cm=0.5 kg4200 J/kgC(30C25C)0.2 kg(150C30C)
Calculate the value of cm :

cm=21000 J/kg2400 K=437.5 J/kgC

So, the specific heat cm of the metal is approximately.

Hence, the answer is the option (3).

Summary

The way of mixtures is frequently used to find out what the specific heat of a liquid is. The sample liquid with a known mass is mixed with a known substance of specific heat at a known temperature. After mixing, the ultimate equilibrium temperature is noted down. Based on the conservation of energy principle, the quantity of heat lost by the hotter substance will always be equal to that gained by the colder liquid.

Frequently Asked Questions (FAQs)

Q: Why is it important to consider the effect of convection currents within the liquids during mixing?
A:
Convection currents within the liquids can affect the rate and uniformity of heat transfer. Proper stirring helps overcome natural convection patterns and ensures more uniform temperature distribution. Understanding and managing these currents is important for achieving accurate and consistent results.
Q: How does the concept of thermal resistance apply to the calorimeter design in this experiment?
A:
Thermal resistance in the calorimeter design affects how well it insulates the mixture from the surroundings. Higher thermal resistance (better insulation) reduces heat loss, improving the accuracy of the experiment. This concept is crucial in designing effective calorimeters for precise measurements.
Q: What is the significance of the heat capacity ratio between the unknown liquid and water in this experiment?
A:
The heat capacity ratio between the unknown liquid and water affects the magnitude of temperature changes observed. If the unknown liquid has a much lower specific heat than water, it will experience a larger temperature change, potentially improving measurement accuracy. Conversely, if it's much higher, the temperature change might be small, requiring more precise measurements.
Q: How does the method of mixture demonstrate the concept of thermal equilibrium?
A:
The method of mixture clearly demonstrates thermal equilibrium as the final state where heat transfer ceases and both liquids reach the same temperature. This illustrates the fundamental principle that heat flows from higher to lower temperatures until equilibrium is achieved.
Q: Why is it important to consider the effect of radiation in high-precision versions of this experiment?
A:
In high-precision measurements, even small amounts of heat transfer via radiation can affect the results. This is especially true when working with large temperature differences or when using materials with high emissivity. Accounting for radiative heat transfer can improve the accuracy of specific heat determinations.
Q: How does the concept of thermal diffusivity apply to this experiment?
A:
Thermal diffusivity, which measures how quickly a material can change its temperature, affects how rapidly the liquids reach thermal equilibrium. Liquids with higher thermal diffusivity will equilibrate faster, potentially reducing errors due to heat loss over time.
Q: What is the importance of thermal equilibrium time in this experiment?
A:
The thermal equilibrium time is crucial because it affects the accuracy of the final temperature measurement. If readings are taken before true equilibrium is reached, the calculated specific heat will be inaccurate. However, longer equilibrium times increase the chance of heat loss to surroundings.
Q: Why is it important to consider the effect of evaporation in open-system versions of this experiment?
A:
In open-system versions, evaporation can lead to additional heat loss from the liquid surface. This heat loss due to evaporation can cause errors in temperature measurements and specific heat calculations, especially for volatile liquids or when working with higher temperatures.
Q: What is the significance of the heat transfer coefficient in this experiment?
A:
The heat transfer coefficient affects the rate at which heat is transferred between the liquids and between the mixture and the calorimeter. A higher coefficient leads to faster heat transfer and quicker attainment of thermal equilibrium, potentially reducing errors due to heat loss to surroundings.
Q: How does the specific heat capacity of a liquid change with temperature, and why is this important for the experiment?
A:
The specific heat capacity of most liquids changes slightly with temperature. This variation is usually small over the temperature ranges used in this experiment but can become significant for very precise measurements or large temperature differences. It's important to be aware of this potential source of error in advanced studies.
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