Question #1 : What is the formula that relates the temperature change obsereved
ID: 634714 • Letter: Q
Question
Question #1 : What is the formula that relates the temperature change obsereved in a substance with the energy released or abosrbed?
#2: when you measure a temperature rise during a chemical reaction, is the reaction endothermic or exothermic?
#3 The enthalpy of the reaction for the reaction of calcium oxide with hydrochloric acid is exothermic. Will the reverse reaction have a positive or negative delta H?
#4 Hess's law allows us to combine reactions to determine the heat of reaction for a net reaction that has not been measured. For the reactions described in the lab, the second reaction is difficult to measure as written. You will measure the heat of reaction for the reverse reaction. How will you use the measurment in the Hess's law calculations?
#5 In part A of this lab you are reacting approximately 0.5g of Mg. In part B, you are directed to use a molar equivalent of MgO for the reaction. What is the molar equivalent of MgO when comparing to 0.5g Mg? Can you think of any reasons why this might be important?
Explanation / Answer
1)q = C x m x (Tf- Ti), where q is heat absorbed or released, C is specific heat, m is mass in grams, and (Tf- Ti) is change in temperature (Tf= final temp, Ti= initial temp).
2)when heat is given off - that is anexothermic reactions(reaction feels warm)
when heat is absorbed, this is anendothermic reaction, so the reaction will feel cold,
Hence a rise in temperature of the reaction is exothermic
3) deltaH is more positive for endothermic reaction
deltaH is more negative for exothermic reactions,
so if the forward reaction is -deltaH, then the reverse will be +deltaH.
4) suppose we have 4 reactions.determine the heat of reaction for reactions 1 and 2 experimentally, then use the known value of Delta H3 to calculate Detla H4. Be aware that equation (2) is the reverse of the reaction you actually run and measure.
5) 0.83g of MgO is the molar equivalent of MgO.
This is important because for the calculation of heat of reaction involving MgO mass of substance is required. which is to be used further in hess's law for calculating the heat of reaction of a certain reaction