Question

A calorimeter is similar to what apparatus used in households? 1) 2) What is the initial temperature of a metal heated to boiling? Calculate the heat generated when 150.0 g of a metal with a specific heat of 2.190 J/ g "C is cooled 3) from 110.0 °C to 34.2 °C. 4) Explain how many significant figures should be expressed in #3 and why. 5) What is the difference between endothermic reactions and exothermic reactions? Give examples of each.

Answer 1

1. Styrofoam Cup. It is a Good insulator and It is used for holding the warmth of the coffee. With the help of styrofoam calorimeter, the temperature of the substance inside the cup can be measured and the temperature is measured after the reaction completes.

2.The process of boiling and heating of the metal can be explained with specific heat. Specific which is calculated by calorimetry. In this case, metal is heathed in boiling water and as boiling water has temp. 100°C which is Boiling point of water. Hence initial temp. Will be 100°C.

3. Heat released, q = m x C x dT

m- mass of substance

c - specific heat

dT- change in temp.

q= 150 x 2.190 x (34.2-110.0)

q= - 24900.3 J =

Here negative sign denotes - Heat is released.

4. There are 6 significant numbers.

2, 4,9,0,0,3

Zeroes between non zero numbers are significant.

5. Endothermic Reactions : The reactions which involve consumption of heat by the reactants ( Heat is given) to form new products are called endothermic reactions

For eg. Melting of ice cubes

Enthalpy change (ΔH) is positive

Entropy change(ΔS) is negative i.e randomness in arrangement

Exothermic reactions : The reactions in which reactants react with each other and produce / release heat along with the products are called Exothermic reactions.

For eg. mixing of quick lime with water, it produces heat by own

Enthalpy change is negative

And entropy change is positive.