Question

A. If 0.96 kg of iron at 120°C is added to 0.75 kg of water at 20°C, what will be the final temperature of the system?

b. By touching the side of a beaker, a student concludes that an endothermic change is taking place inside it. Write 2 - 3 sentences explaining how the student came to that conclusion and comparing the energy o the products of an endothermic reaction with the energy of the reactants.

c. As a substance freezes, its temperature does not change. How does the potential energy of the molecules of the substance change as a result of the heat released? What type of energy must decrease in order for the temperature to decrease?

Answer 1

31.38 °C will be the final temperature of the system.

Step-by-step explanation:

a) Heat lost by iron will be equal to heat gained by the water

`-Q_1=Q_2`

Mass of iron =
`m_1=0.96 kg = 960 g`

Specific heat capacity of iron =
`c_1=0.450 J/g^oC`

Initial temperature of the iron =
`T_1=120^oC`

Final temperature =
`T_2`=T

`Q_1=m_1c_1* (T-T_1)`

Mass of water=
`m_1=0.75 kg = 750 g`

Specific heat capacity of water=
`c_2=4.186 J/g^oC`

Initial temperature of the water =
`T_3=20^oC`

Final temperature of water =
`T_2`=T

`Q_2=m_2c_2* (T-T_3)`

`-Q_1=Q_2`

`-(m_1c_1* (T-T_1))=m_2c_2* (T-T_3)`

On substituting all values:

we get, T = 31.38 °C

31.38 °C will be the final temperature of the system.

b) During an endothermic reaction, energy is absorbed from the surroundings and temperature of the surrounding decreases.The energy of the reactants are less than that of the energy of the products.

If the reaction is an endothermic , then the surrounding that is beaker will cool down due to lowering in lower in temperature.This lowering down of temperature is due to the absorption of kinetic energy of the particles in the system by products.

c) When the substance is freezes its potential energy increases . Energy is released when substance freezes and this energy is termed as latent heat of freezing.

Also with decrease in temperature of the of substance the kinetic energy of the particles decreases as we know that temperature and kinetic energy are directly related. And with decrease in kinetic energy the potential energy of the substance particle will increase as per as law of conservation of energy.

Answer 2

PART A)

Heat released by iron = heat gain by water

now we have

`m_1s_1(\Delta T_1) = m_2s_2(\Delta T_2)`

`0.96(450)(120 - T) = 0.75(4186)(T - 20)`

`120 - T = 7.27(T - 20)`

`120 - T = 7.27T - 145.3`

`T = 32.1 degree C`

PART B)

When endothermic changes takes place in the system then system absorbs the energy from its surrounding and keeps on cooling down

Due to this the observer will feel the cool down of the surface temperature and conclude that it is an endothermic reaction

PART C)

When a substance freezes its temperature do not change but if we will check the potential energy of molecules we can conclude that the system released its energy which is known as latent heat.

This will lead to the increase in its potential energy

And due to this decrease in latent heat the substance will freeze