Question

calcium oxide has been proposed as a substance. calculate the minimum mass of CaO that would be required to cause this temperature change

Answer 1

The question is incomplete. Here is the complete question.

Calcium oxide,
`CaO_((s))`, has been proposed as a substance that can be used to heat water quickly for portable heating packs or for cooking. When placed in water,
`CaO_((s))` reacts as shown by hte equation below:

`CaO_((s))+H_(2)O_((l))` ⇄
`Ca(OH)_(2)_((s))`

a) A student wants to design a heating pad that could heat a 150.0 g sample of water from 25.0°C to 60.0°C.

(i) Calculate the amount of heat, in joules, that the water must absorb for its temperature to change by this amount. (Assume that specific heat capacity of water is 4.18J/(g.°C).)

(ii) Calculate the minimum mass of
`CaO_((s))` that the student would need to use in order to cause this temperature change.

Answer: (i) Q = 21,945J

(ii) m = 467.87g

Step-by-step explanation: Energy necessary for the water to absorb to heat up is calculated by:

`Q=mc\Delta T`

Q is heat

c is specific heat capacity, in this case in J/g.°C

`\Delta T` is change in temperature

(i) Calculating amount of heat:

`Q=150*4.18*(60-25)`

Q = 21945J

The water needs 21,945 joules to increase by that amount of temperature.

(ii) According to the chemical equation:

`CaO_((s))+H_(2)O_((l))` ⇄
`Ca(OH)_(2)_((s))`

it is needed 1 mol of each reagent to produce 1 mol of product.

Molar mass of water is 18g/mol. For 150g, there are:

n =
`(150)/(18)`

n = 8.34 mols

Molar mass of CaO is 56.1g/mol. For 8.34 mols:

m = 8.34*56.1

m = 467.87g

For calcium oxide to increase temperature in 35°C, the minimum necessary is 467.87 grams.