ΔcHmØ (石墨)= -393.7 kJ/mol,ΔcHmØ (金刚石)= -395.8 kJ/mol,则反应C(石墨) = C(金刚石)的焓变应为
A. -789.5 kJ/mol
B. -2.1 kJ/mol
C. +2.1 kJ/mol
D. +789.5 kJ/mol
按通常规定,标准生成热为零的物质有
A. N2(l)
B. Na(g)
C. 红磷(s)
D. Hg (l)
如果体系经过一系列变化后又回到初始状态,则体系的
A. Q =0 ,W =0 ,ΔU =0, ΔH =0
B. Q ≠0, W ≠0 ,ΔU =0, ΔH =0
C. Q = -W, ΔU = Q+W, ΔH =0
D. Q= W,U = Q+W ,ΔH =0
下列反应中,ΔrSmΘ>0 的是
A. 2 H2(g)+O2(g) = 2 H2O(g)
B. N2(s)+3 H2(g) = 2 NH3(g)
C. NH4Cl(s)=NH3(g)+HCl(g)
D. C(s)+O2(g) = CO2(g)