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The molar heat capacity of a certain substance varies with temperature according to the empirical equation C=29.5J/molK+(8.20×103J/molK2)T How much heat is necessary to change the temperature of 3.00 mol of this substance from 27C to 227C? (Hint: Use Eq. (17.18) in the form dQ = nC dT and integrate.)

Short Answer

Expert verified
The heat necessary is 22107 J.

Step by step solution

01

Identify the Variables

We begin by identifying the given variables:- Initial temperature, Ti=27C=300K- Final temperature, Tf=227C=500K- Number of moles, n=3.00mol- Molar heat capacity, C=29.5J/molK+(8.20×103J/molK2)T
02

Setup the Heat Transfer Equation

Using the hint provided, we know that the differential form of the heat transfer can be expressed as dQ=nCdT. This tells us how much heat is added when the temperature changes by an infinitesimal amount dT.
03

Substitute the Molar Heat Capacity into the Equation

Replace C with the given function: dQ=3.00(29.5+(8.20×103)T)dTThis modifies dQ in terms of T.
04

Integrate the Equation

Calculate the total heat Q by integrating dQ from Ti=300K to Tf=500K:Q=3005003.00(29.5+(8.20×103)T)dTSolving the integral:Q=3.00[29.5T+8.20×1032T2]300500
05

Evaluate the Integral

Evaluate the integrated function at the bounds:Q=3.00[(29.5×500+8.20×1032×5002)(29.5×300+8.20×1032×3002)]This simplifies to:Q=3.00[14750+1.025×5002(8850+1.025×3002)]
06

Calculate the Numerical Value

Calculate each term inside the brackets:- 29.5×500=14750- (8.20×103/2)×5002=1025- 29.5×300=8850- (8.20×103/2)×3002=369Substitute these values back into the equation to find Q:Q=3.00((14750+1025)(8850+369))Q=3.00×7369=22107J
07

Conclusion

The total heat required to change the temperature of the substance is 22107 J.

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Key Concepts

These are the key concepts you need to understand to accurately answer the question.

Molar Heat Capacity
Molar heat capacity is an important concept in thermodynamics as it measures the amount of heat a substance can hold per mole for a given temperature change. Expressing it as a function of temperature, like in the provided equation, is common for many substances. This equation describes how the heat capacity changes depending on the temperature, combining a constant term and a temperature-dependent term:
  • The constant term (29.5 J/mol·K) represents the basic heat absorption ability inherent to the substance, regardless of temperature.
  • The temperature-dependent term 8.20×103T reflects how the capacity increases or decreases as the substance's temperature changes.

In this way, molar heat capacity is crucial for determining how much heat is needed during a temperature change, thus playing a central role when calculating heat transfer in varying thermal conditions.
Temperature Change
Temperature change is simply the difference between the initial and final temperatures of a substance when it undergoes heating or cooling. In thermodynamic calculations, temperature is typically converted from Celsius to Kelvin for accuracy.
  • The initial temperature, Ti, is where the process starts; for this exercise, it is 27°C or 300 K.
  • The final temperature, Tf, is the end point of the process, which in this exercise is 227°C or 500 K.

The temperature change, ΔT, is the difference TfTi=500K300K=200K. This change is a driving force in the thermodynamic equations, affecting the amount of heat transfer required to achieve that change.
Heat Transfer
Heat transfer is the movement of thermal energy from one place to another. In a thermal system, it is often calculated using the relation dQ=nCdT, where dQ is the differential heat added, n is the number of moles, C is the molar heat capacity, and dT is the small change in temperature. This relation tells us how heat added depends on the thermal properties of the substance and the current temperature.
  • In our case, the number of moles, n=3.00, affects how much total heat is required.
  • The molar heat capacity, expressed as 29.5+(8.20×103)T, is substituted into this formula, creating a differential equation ready to be integrated.

This calculated heat transfer quantifies the energy needed to achieve the desired temperature change, playing a vital role in thermal management and engineering.
Integration in Thermodynamics
Integration in thermodynamics allows for calculating the total heat transfer over a finite range of temperatures. Starting with the expression dQ=nCdT, we integrate both sides from the initial temperature Ti to the final temperature Tf.
  • This involves integrating the molar heat capacity equation over the temperature range. Here, Q=3005003.00(29.5+(8.20×103)T)dT.
  • The integral evaluates to Q=3.00[29.5T+8.20×1032T2]300500.

Solving this integral provides the total heat required, using fundamental calculus that bridges changes in state functions across temperature ranges. This method is essential for accurately determining energy exchanges in chemistry and physics.

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Most popular questions from this chapter

Rods of copper, brass, and steel-each with crosssectional area of 2.00 cm2-are welded together to form a Y-shaped figure. The free end of the copper rod is maintained at 100.0C, and the free ends of the brass and steel rods at 0.0C. Assume that there is no heat loss from the surfaces of the rods. The lengths of the rods are: copper, 13.0 cm; brass, 18.0 cm; steel, 24.0 cm. What is (a) the temperature of the junction point; (b) the heat current in each of the three rods?

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