Answer:
The reaction D has the value of ΔH°rxn equal to ΔH°f for the product.
Explanation:
The ΔH°f for product is equal to ΔH°rxn when the reagents are in their elemental state (ΔH°f = 0) and form one mole of product.
We have to find the reagents that are in their elemental state and that only form one mole of product:
A) 2Ca (s) + O₂ (g) → 2CaO (s)
The reagents are in their elemental state but the reaction forms two mole of product.
B) C₂H₂ (g) + H₂ (g) → C₂H₄ (g)
C₂H₂ (g) is not in its elemental state.
C) 2C (graphite) + O₂ (g) → 2CO (g)
Graphite and Oxygen are in their elemental state but the reaction forms two mole of product.
D) 3Mg (s) + N₂ (g) → Mg₃N₂ (s)
Magnesium and Nytrogen are in their elemental state and the reaction forms one mole of product.
E) C (diamond) + O₂ (g) → CO₂ (g)
Diamond is not in its elemental state.
Answer:
Enamel is there to protect teeth from decay and damage. Every time you eat and drink, you expose your teeth to acids and bacteria from your food. This would seriously harm teeth if it weren't for enamel.
Explanation:
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Your question is not complete as you have omitted some significant values in the question. Please let me assume this to be your question;
QUESTION;
Understanding the enthalpy definition=
Measurements show that the enthalpy of a mixture of gaseous reactants increases by 125.kJ during a certain chemical reaction, which is carried out at a constant pressure. Furthermore, by carefully monitoring the volume change it is determined that -71.kJ of work is done on the mixture during the reaction. Calculate the change in enthalpy of the gas mixture during the reaction and determine if the reaction is endothermic or exothermic.
ANSWER: The change in enthalpy of the gas mixture during the reaction is 54.kJ
The reaction is endothermic.
EXPLANATION: Enthalpy is the heat change in a system.
To calculate enthalpy we use the formula below;
H = E + PV
H is the enthalpy
E is the energy used in the reaction
PV is the product of pressure and volume which is refered to as the work done in the system
Using the equation above
H = 125 + (-71) = 54.kJ
An endothermic reaction is a type of reaction where heat is gained by the system from it's environment, and the enthalpy of such system is positive. While an Exothermic reaction is a type of reaction where heat is lost by the system to it's environment, and the enthalpy of such system is negative.
Because our enthalpy value is positive, this is an endothermic reaction.