# First Law of Thermodynamics and automobile

• Gil-H
I right?In summary, the conversation discusses the process of an automobile battery discharging and then being recharged to its initial state. Through the use of the first law of thermodynamics, it is determined that the battery must dissipate 584kJ of heat to the environment during the charging process. However, the given answer in the book is +440kJ, which may be incorrect.

## Homework Statement

An automobile battery that is originally fully charged gradually discharges while sitting on a shelf at a constant temperature of 40C, producing no electric work but resulting in a heat transfer of 1000kJ to its enviroment.
The battery is then recharged to its initial state by means of a process involving work input of 440Wh.
Find the heat interaction of the battery during this charging process. Justify your answer thermodynamically.

## Homework Equations

The first law of thermodynamics
ΔE = Q -W

## The Attempt at a Solution

in the first step, heat is moving out of the system and no work is done, so:
Q12 = -1000kJ
W12 = 0

in the charging process, the is done on the system, so:
W21 = -440Wh = -440[Wh]*3.6[kJ/Wh] = -1584kJ

The battery is charged to its initial state, so:
ΔE = 0
ΔE12 + ΔE21 = 0
(Q12 - W12) + (Q21 - W21) = 0
-1000kJ + Q21 +1584kJ = 0
and
Q21 = -584kJ

the answer in the book is +440kJ. Why? What have I done wrong?

I am not sure what is meant by "heat interaction" of the battery.

If the battery in its initial state can supply 1000KJ of energy to its environment by discharging, and if 1584KJ (440Wh) of work is needed to recharge it to its original state (original charge and temperature), then the battery must dissipate 584KJ of heat to the environment in the charging process. $\Delta Q = \Delta U + W = 1000KJ - 1584KJ = -584KJ$ (W = +work done BY the battery)

I would say the answer given is wrong and you are correct.

AM

## What is the First Law of Thermodynamics?

The First Law of Thermodynamics is a fundamental principle in physics that states that energy cannot be created or destroyed, but can only be transferred or converted from one form to another. In the context of an automobile, this means that the energy used to power the car (i.e. the gasoline) is not created or destroyed, but is instead converted into the energy needed to move the car.

## How does the First Law of Thermodynamics apply to an automobile?

In an automobile, the First Law of Thermodynamics is evident in the process of combustion. When fuel is burned, it releases chemical energy which is then converted into thermal energy. This thermal energy is then converted into mechanical energy that is used to power the movement of the car.

## What is the role of the engine in the First Law of Thermodynamics and an automobile?

The engine in an automobile is responsible for the conversion of energy according to the First Law of Thermodynamics. It takes the chemical energy from the fuel and converts it into mechanical energy that powers the movement of the car. This process also produces waste heat, which is why engines can become hot during operation.

## How does the First Law of Thermodynamics impact fuel efficiency in automobiles?

The First Law of Thermodynamics plays a crucial role in fuel efficiency in automobiles. Since energy cannot be created or destroyed, any energy that is not converted into mechanical energy to power the car will be lost as waste heat. Therefore, the more efficient an engine is in converting fuel into mechanical energy, the better the fuel efficiency of the automobile will be.

## What are some real-world applications of the First Law of Thermodynamics and automobiles?

In addition to powering cars, the First Law of Thermodynamics is also important in understanding the efficiency of different types of engines and fuels. It is also essential in the development of new technologies, such as hybrid and electric cars, which aim to improve fuel efficiency and reduce waste heat. Additionally, the First Law of Thermodynamics is crucial in understanding the impact of transportation on the environment and how it contributes to global energy consumption.