Tomorrow i have a test, I with these questions

[Roro312]

Tomorrow is my test and i understand partially everything... and than i stumbled upon these two questions and if i just know what's used for each formula .. i can do it

1) Calculate the amount of energy required to evaporate an ice cube having a mass of 45g.

I know that first it must go for solid to liquid which is E=mf and than from liquid to gas which is E=mLv .. can someone please show me how to do them... my test is tomorrow:(

Lf water= 3.3x10^5 J/Kg
water=4.2x10^3 J/Kg'C
ice= 2.1x 10^3 J/Kg'C

the other question i didnt get was:

2)An 80g mandarin orange is burned in bomb calorimeter. The 1.55 kg of water change in temperature from 21.0'C to 39.4'C. Calculate the energy per gram in the mandarin orange.


I would show you my attempt except its just ridiculous becuase i reallyyyy don't get it.


Your help is muchhhh appreciated.. i need help ASAP ...thank you

 

[rock.freak667]

Well for the first one, you will need energy to

1)convert the ice to liquid which is (solid to liquid)
2) Raise the temperature to the boiling point of water
3) convert all the liquid to vapor

So find the individual energy requirements and add them up.


For the second one, how much energy would it take to raise the temperature of water of mass 1.55kg from 21C ro 39.4C?.

 

[Roro312]

Thats the problem... i don't know how to convert solid to liquid.. what formula do i use?

 

[Gravitino22]

Q=mC C is a constant you can look up for water its different depending on which phase transition you are calculating.
Q=mc(Tf-Ti) for when your raising the temperature c i think its 1cal/gC for water.

Add all the Qs and viola

 

[rdl]

Dear student,

I understand that you are facing difficulties with these two questions and your test is tomorrow. Don't worry, I will try my best to explain the concepts and equations needed to solve them.

For the first question, you are correct in using the equations E=mf and E=mLv. Let's break down the steps to solve this problem:

Step 1: Convert the mass of the ice cube from grams to kilograms. Remember, the units in equations must be consistent. So, 45g = 0.045kg.

Step 2: Calculate the energy required to melt the ice cube using the equation E=mf. Since we are going from solid to liquid, we will use the latent heat of fusion (Lf) for water, which is given in the question as 3.3x10^5 J/kg. So, E = (0.045kg)(3.3x10^5 J/kg) = 14850 J.

Step 3: Calculate the energy required to vaporize the water using the equation E=mLv. Since we are going from liquid to gas, we will use the latent heat of vaporization (Lv) for water, which is not given in the question. However, we can find it by using the specific heat capacity (C) of water, which is given as 4.2x10^3 J/kg'C. The equation to find Lv is Lv = C x (Tf-Ti), where Tf is the final temperature (100'C) and Ti is the initial temperature (0'C). So, Lv = (4.2x10^3 J/kg'C)(100-0) = 420000 J/kg.

Step 4: Calculate the total energy required to evaporate the ice cube by adding the energy required to melt and the energy required to vaporize. E = 14850 J + 420000 J = 434850 J.

For the second question, we are given the mass of the mandarin orange (80g) and the change in temperature of the water (21.0'C to 39.4'C). We need to use the equation Q=mcΔT, where Q is the energy, m is the mass, c is the specific heat capacity, and ΔT is the change in temperature.

Step 1: Convert the mass of the mandarin orange from grams to kilograms. So, 80g = 0.08kg