Enthalpy of a reaction

a) This reaction is an exothermic reaction. $\color{#3D99F6}{True}$

• An exothermic reaction releases energy such as heat to the surroundings. The graph shows that the reactants $\ce{CH4}$ and $\ce{O2}$ have a higher energy than that of the products $\ce{CO2}$ and $\ce{H2O}$ . Therefore, the reaction releases energy, which is heat, to the surroundings and it is exothermic.

b) The temperature of surroundings goes down when the reaction occurs. $\color{#D61F06}{False}$

• As heat is released to the surroundings, it raises its temperature and lowers it. Whereas, an endothermic (the opposite of exothermic) reaction absorbs heat from the surroundings and lower its temperature.

c) The enthalpy of reactants is greater than that of products. $\color{#3D99F6}{True}$

• Enthalpy $H$ is a measure of energy. As the reactants have a higher energy level therefore a higher enthalpy than that of reactants. For an exothermic reaction, enthalpy change $\Delta H = H_{products} - H_{reactants} > 0$ (negative), therefore, $H_{reactants} > H_{products}$ .

d) The magnitude of enthalpy change when $8$ g of $\ce{CH4}$ is completely combusted is $890.8$ kJ. $\color{#D61F06}{False}$

• The enthalpy change $\Delta H$ is $-890.8$ kJ per mole or $16$ g of $\ce{CH4}$ , but $8$ g is only half a mole.

basic question