Specific Heat 4/28/17

Heat is the ___Transfer___ of energy due to a change in temperature OUCH! Why can you still burn your fingers by touching the metal handle of a pot on the stove even when the water is only lukewarm? The heat is still there…in the water. It holds 10x’s more heat than the iron pot! The __Specific Heat __ of water is very high; it takes a lot of energy to raise one gram of water 1 degree Celsius.

Calories to Joules _1_calorie = 4.185 Joules 1 kilocalorie = ___1000____ calories. ( a kilocalorie is the same thing as “big C” Calorie)

SPECIFIC HEAT CAPACITY The amount of heat (in calories or Joules) that must be added or removed from a __gram___ of that substance to change its temperature by ____1˚C__. WHEN THERE IS HEAT/ENERGY INVOLVED:  Q (heat energy) = m (mass) x Δt (temp.) x cp (specific heat capacity) (cal/Joules) (g) (°C) (cal/g °C) or (Joule/g °C)

Problem 1 How much heat energy is needed to raise the temperature of 100 grams of water from 0 degrees to 30° C? (the specific heat of water is 4.18 J/(g°C) Find your variables: Q=? m= 100 g ΔT= 30° C - 0° C = 30° C Cp = 4.18 J/(g°C) Solve for Q… 12,540 J or 12.54 KJ

Problem 2 A calorimeter contains 300 grams of water at 10° C. After a food sample is burned in the calorimeter the water temperature changes to 15° C. How much heat was given off by the food sample? Can you recall the specific heat of water from the last problem?? You’re going to need it.

Problem 3 What amount of heat is required to raise the temperature of 85.9 g of water by 7C? The specific heat of water is 4.184 J/gC.

Problem 4 What amount of heat is required to increase the temperature of 75.0 g of water from 22.3C to 36.1C? The specific heat of water is 4.184 J/gC.

Problem 5 How much energy is required to increase the temperature of 100 grams of water from 25 C to 85 C?

Problem 6 How much water can absorb 2500 calories of heat if the temperature changes 5 degrees? Can we use the specific heat value for water we have been using (4.18 J/gC.) ? No we cannot! The Problem asks for calories not Joules. We must use 1 c/g °C

Problem 7 q(water) = m c (T-22.3) q(silver) = m c (T-100) You place 300.0 g of water in a coffee-cup calorimeter and the temperature of the water is 22.3C. A 94.5 g piece of silver metal is heated to 100.0C and added to the water in the calorimeter. What will the final temperature of the silver and the water be? The specific heat of silver is 0.235 J/gC. q(water) = m c (T-22.3) q(silver) = m c (T-100) set the two equations equal to each other q(water)= -q(silver)